Methods of making a prosthesis with a smooth covering

ABSTRACT

The present invention relates to methods of making a prosthesis or a stent with a smooth covering. The method includes providing an elastomeric tube including an inner diameter and an outer diameter, positioning the elastomeric tube in a tube expander including a vacuum, expanding the inner diameter and the outer diameters of the elastomeric tube by applying the vacuum, providing a mandrel, positioning an inner covering over the mandrel, positioning a stent over the inner covering, positioning an outer covering over the stent to form a covered stent, positioning the mandrel and the covered stent in the tube expander, releasing the vacuum, removing the elastomeric tube, the covered stent, and the mandrel form the tube expander, applying pressure and heat to the elastomeric tube, the covered stent, and the mandrel, removing the elastomeric tube, the covered stent, and the mandrel from the pressure and the heat, removing the elastomeric tube from the covered stent, and removing the mandrel from the covered stent.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/224,101, filed on Jul. 29, 2016, which claimsthe benefit of the filing date under 35 U.S.C. § 119(e) of ProvisionalU.S. Patent Application Ser. No. 62/199,764, filed on Jul. 31, 2015, thecontents of which are hereby incorporated by reference in theirentireties.

BACKGROUND 1. Technical Field

The present invention relates to methods of making a prosthesis with asmooth covering.

2. Background Information

Some medical prostheses, such as stents, include material, fabric or agraft to cover the prosthesis. Covered stents include a stent graft thatincludes fabric or other material that covers and is supported by astent. Covered stents are manufactured by different methods. One methodincludes placing the stent on a mandrel between shells of a pressureapplicator. The pressure applicator may include two halves or multiplecomponents that form a cavity with a circular cross section. Eachcomponent of the pressure applicator may contain one or more layers ofmaterial for application to the stent. When the components of thepressure applicator are brought together to cover the stent, theresulting covered stent may have visible creases where the componentsmeet. The creases create a lack of continuity in the material coveringthe stent and may cause premature failure of the material or an areathat may catch on a vessel or collect undesirable material.

Other methods of manufacturing covered stents include using shrink tubesand/or tubing that are off the shelf and readily available to attach thefabric or graft on the stent. For example, covered stents have been madeusing off the shelf silicone tubing having a high durometer, such ashigh durometer silicone tubing including silicone tubing with adurometer of 50-70 Shore A. Manufacturers identify silicone tubinghaving a durometer of 50-70 Shore A as soft and silicone tubing having adurometer of 35-45 Shore A as very soft, both of which are readilyavailable from manufacturers. Silicone tubing with a lower durometer isnot readily available from manufacturers.

These methods to make covered stents using shrink tubes, tubing having ahigh durometer, and/or sheets of material having a high durometer toattach the fabric or graft on the stent may create visible creases orridges that form on the graft of the stent, which create a lack ofcontinuity on the stent. Previously used pressure methods also cause thestruts of the stent to deform or distort when the shrink tubes or highdurometer tubes are applied to the fabric and the stent because higherdeformation forces and displacement of the tubes is needed to compressthe fabric or graft around the struts of the stent for bonding. Inaddition, when using these methods, the fabric or graft is not able toconform to the struts of the stent, or otherwise profile the struts ofthe stent, to create a smooth covering over the stent.

BRIEF SUMMARY OF THE INVENTION

A method of making a stent with a smooth covering is described. Themethod includes using a low durometer elastomeric tube, preferably a lowdurometer silicone tube, in the method of making a covered prosthesis.

One exemplary method includes positioning the elastomeric tube in a tubeexpander, and applying a vacuum to the tube expander to increase boththe inner and outer diameters of the elastomeric tube. In one example, amandrel is then provided with an inner covering. A stent is positionedover the inner covering, and then an outer covering is positioned overthe stent to form a covered stent. In some examples, only an innercovering may be used or only an outer covering may be used. The mandreland the covered stent are placed in the tube while the elastomeric tubeis still in the tube expander, and the vacuum is released. Release ofthe vacuum causes the elastomeric tube to return to its previousdiameter. The elastomeric tube, the covered stent, and the mandrel arethen removed from the tube expander. Pressure and heat are applied tothe elastomeric tube, the covered stent, and the mandrel. The pressureand heat are then removed. The elastomeric tube is removed from the nowcovered stent and the covered stent is removed from the mandrel.

A variation of the method includes providing a slit cannula including aninner diameter, an outer diameter, and a plurality of slits. A firstelastomeric tube is positioned over the slit cannula, and an innercovering is positioned over the first elastomeric tube. A stent ispositioned over the inner covering. A mandrel is positioned within theslit cannula to expand the first elastomeric tube and the innercovering. A second covering is positioned over the stent. A secondelastomeric tube is provided that includes an inner diameter and anouter diameter, and the second elastomeric tube is positioned in a tubeexpander including a vacuum. A vacuum is applied to expand the innerdiameter and outer diameter of the second elastomeric tube. The coveredstent, the first elastomeric tube, the slit cannula, and the mandrel arethen positioned in the second elastomeric tube within the tube expander,and the vacuum is released. The first and second elastomeric tubes, thecovered stent, the slit cannula, and the mandrel are removed from thetube expander, and heat and pressure are applied to the first and secondelastomeric tubes, the covered stent, the slit cannula, and the mandrel.The first and second elastomeric tubes, the covered stent, the slitcannula, and the mandrel are removed from the pressure and the heat, andthe second elastomeric tube is removed from the covered stent. Themandrel is removed from the slit cannula, and the covered stent isremoved from the first elastomeric tube and the slit cannula.

Another variation includes encapsulating a prosthesis with a smoothcovering. The method includes providing a mandrel and positioning afirst covering over the mandrel. A prosthesis is positioned over thefirst covering, and a second covering is positioned over the prosthesisto form a covered prosthesis. A first tube is provided that includes aninner diameter and an outer diameter, and the first tube is positionedin a tube expander including a vacuum. A vacuum is applied to the tubeexpander to expand the inner and outer diameters of the first tube. Thecovered prosthesis and the mandrel are positioned in the tube expander,and the vacuum is released. The first tube, the covered prosthesis, andthe mandrel are removed from the tube expander. A second tube isprovided that includes an inner diameter and an outer diameter. Theinner diameter of the second tube is smaller than the inner diameter ofthe first tube. The second tube is positioned over the first tube, andheat is applied to the first and second tubes, the covered prosthesis,and the mandrel. The first and second tubes, the covered prosthesis, andthe mandrel are removed from the heat, and the second tube is removedfrom the first tube, the covered prosthesis, and the mandrel. The firsttube is removed from the covered prosthesis and the mandrel, and themandrel is removed from the covered prosthesis.

These methods provide, among others, the advantages of making a stent ora prosthesis with a covering that conforms to the struts of the stent orprosthesis, has a smooth covering, has no visible creases that formwithin the covering of the stent of prosthesis, and has a smoothcovering that does not distort or deform the struts of the stent orprosthesis.

These methods also provide the advantages of making a stent or otherprosthesis with a smooth inner surface and an outer surface thatconforms to the struts of the stent or other prosthesis, which is notexposed to blood flow in the body. Therefore, the likelihood ofturbulent blood flow and associated stagnation points is reduced withstents or other prosthesis formed by these methods.

At least one unique and important feature of the methods is that thetube used to apply the covering to the stent has a very low durometer onthe Shore A or Shore 00 scale. Such low durometer tubes are not standardand not readily or commercially available from manufacturers. These lowdurometer tubes allow sufficient pressure to be applied to the stent orother prosthesis to displace the tube around the struts of the stent andensure contact of the inner and outer coverings for increased surfacearea for bonding the inner and outer coverings without distorting ordeforming the stent or other prosthesis.

The accompanying drawings, which are incorporated herein and constitutepart of this specification, and, together with the general descriptiongive above and the detailed description given below, serve to explainfeatures of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of an example of expanding anelastomeric tube by positioning the elastomeric tube in a tube expanderto expand the elastomeric tube;

FIG. 2 shows a cross-sectional view of FIG. 1;

FIG. 3 shows a perspective view of wrapping the elastomeric tube aroundthe ends of the tube expander to seal the elastomeric tube to the tubeexpander;

FIG. 4 shows a cross-sectional view of FIG. 3;

FIG. 5 shows a perspective view of connecting a vacuum source to a portof the tube expander;

FIG. 5A shows an example of rings positioned over the elastomeric tubeto seal the elastomeric tube to the tube expander;

FIG. 5B shows an example of caps positioned over the elastomeric tube toseal the elastomeric tube to the tube expander;

FIG. 6 shows a perspective view of applying the vacuum source to thetube expander;

FIG. 7 shows a cross-sectional view of FIG. 6 after the vacuum sourcehas been applied;

FIGS. 8 and 9 show perspective views of positioning a mandrel with astent with inner and outer coverings in the elastomeric tube in the tubeexpander;

FIG. 10 shows a cross-sectional view of FIG. 9;

FIG. 10A shows a partial exploded view of FIG. 10;

FIG. 11 shows a perspective view of releasing the vacuum source from thetube expander;

FIG. 12 shows a cross-sectional view of FIG. 11 after the vacuum sourcehas been released;

FIG. 12A shows a partial exploded view of FIG. 12;

FIG. 13 shows a perspective view of removing the elastomeric tube, themandrel, and the stent with inner and outer coverings from the tubeexpander;

FIG. 14 shows a cross-sectional view of FIG. 13;

FIG. 15 shows a perspective view of positioning the elastomeric tube,the mandrel, and the stent with inner and outer coverings in a pressfixture;

FIG. 15A shows a perspective view of an example of sleeves positionedover the mandrel;

FIG. 16 shows a perspective view of the elastomeric tube, the mandrel,and the stent with inner and outer coverings in the press fixture;

FIG. 17 shows a cross-sectional view of FIG. 16;

FIG. 17A shows a partial exploded view of FIG. 17;

FIG. 18 shows a perspective view of applying heat and pressure to thepress fixture;

FIG. 19 shows a cross-sectional view of FIG. 18;

FIG. 19A shows a partial exploded view of FIG. 19;

FIG. 20 shows a perspective view of the elastomeric tube, the mandrel,and the stent after removal from the press fixture;

FIG. 21 shows a cross-sectional view of FIG. 20;

FIG. 22 shows an example of removing the elastomeric tube from the stentby peeling or ripping the elastomeric tube away from the stent;

FIG. 23 shows a side view of the stent after removal of the elastomerictube;

FIG. 24 shows a side view of removing the mandrel from the stent;

FIG. 25 shows a cross-sectional view of the stent with the layer of thefirst material and the second material after removal of the mandrel;

FIG. 26 shows a side view of an example of a slit cannula for use inencapsulating a stent with a stent mandrel assembly;

FIG. 27 shows a cross-sectional view of FIG. 26 of a first end of theslit cannula;

FIG. 28 shows a cross-sectional view of FIG. 26 of a second end of theslit cannula;

FIG. 29 shows a perspective view of FIG. 26;

FIG. 30 shows a perspective view of an example of a first mandrel and asecond mandrel for insertion within the first and second ends of theslit cannula;

FIG. 31 shows a perspective view of positioning the first mandrel withinthe first end of the slit cannula;

FIG. 32 shows a perspective view of expanding the slit cannula with thefirst mandrel;

FIG. 33 shows a perspective view of a first elastomeric tube over anon-expanded portion of the slit cannula;

FIG. 34 shows a perspective view of an inner covering over theelastomeric tube;

FIG. 35 shows a perspective view of a stent over the inner covering andpositioning the second mandrel within the second end of the slitcannula;

FIG. 36 shows a perspective view of an outer covering over the stent;

FIG. 37 shows an example of removing handles from the first and secondmandrels;

FIG. 38 shows a perspective view of positioning the first and secondmandrels, the slit cannula, the first elastomeric tube, and the stentwith the inner and outer coverings within a tube expander with a secondelastomeric tube;

FIG. 39 shows a perspective view of the first and second mandrels, theslit cannula, the first elastomeric tube, the stent with the inner andouter coverings, and the second elastomeric tube after removal from thetube expander;

FIG. 40 shows a perspective view of FIG. 39 in a press fixture;

FIG. 41 shows a perspective view of FIG. 40 within a heat press;

FIG. 42 shows a perspective view of positioning the first and secondmandrels, the slit cannula, the first elastomeric tube, the smoothcovered stent, and the second elastomeric tube within a tube expanderafter applying heat and pressure;

FIG. 43 shows a perspective view of removing the first and secondmandrels, the slit cannula, the first elastomeric tube, and the smoothcovered stent from the tube expander;

FIG. 44 shows a perspective view of an example of positioning the endcaps on the first and second mandrels;

FIG. 45 shows a perspective view of removing the first and secondmandrels from the slit cannula and removing the smooth covered stentfrom the slit cannula;

FIG. 46 shows a perspective view of the smooth covered stent withstripes or indentations on the inner surface of the smooth coveredstent;

FIG. 47 shows a perspective view of a third mandrel to be inserted intothe smooth covered stent;

FIG. 48 shows a perspective view of the third mandrel with the smoothcovered stent and a first elastomeric tube;

FIG. 49 shows a perspective view of the third mandrel, the smoothcovered stent, and the first elastomeric tube and a second elastomerictube;

FIG. 50 shows a perspective view of the third mandrel with the firstelastomeric tube and the smooth covered stent with the secondelastomeric tube with a press fixture;

FIG. 51 shows a perspective view of FIG. 50 within a heat press;

FIG. 52 shows a perspective view of removing the second elastomeric tubefrom the first elastomeric tube;

FIG. 53 shows a perspective view of positioning a shrink tube over thefirst elastomeric tube;

FIG. 54 shows a perspective view of applying heat to the smooth coveredstent, the first elastomeric tube, and the shrink tube;

FIG. 55 shows a perspective view of removing the shrink tube form thefirst elastomeric tube;

FIG. 56 shows a perspective view of the smooth covered stent without thestripes or indentations on the inner surface of the smooth coveredstent;

FIG. 57 shows a perspective view of an example of the slit cannula andan example of a single mandrel;

FIG. 58 shows a cross-sectional view of FIG. 57;

FIG. 59 shows a perspective view of the single mandrel within the slitcannula;

FIG. 60 shows a cross-sectional view of FIG. 59;

FIG. 61 shows a perspective view of the slit cannula of FIG. 57 with asecond example of a single mandrel;

FIG. 62 shows a cross-sectional view of FIG. 61;

FIG. 63 shows a perspective view of the second example of the singlemandrel within the slit cannula;

FIG. 64 shows a cross-sectional view of FIG. 63;

FIG. 65 shows a perspective view of a covered stent positioned on amandrel;

FIG. 66 shows a perspective view of positioning a first tube in the tubeexpander;

FIG. 67 shows a perspective view of applying a vacuum source to the tubeexpander;

FIG. 68 shows a perspective view of positioning the covered stent andthe mandrel in the tube expander;

FIG. 69 shows a perspective view of releasing the vacuum source from thetube expander;

FIG. 70 shows a perspective view of the first tube, the covered stent,and the mandrel after removal from the tube expander;

FIG. 71 shows a perspective view of positioning a second tube in thetube expander;

FIG. 72 shows a perspective view of applying a vacuum source to the tubeexpander;

FIG. 73 shows a perspective view of the covered stent and the mandrelafter the first and second tubes are applied to the covered stent;

FIG. 74 shows a perspective view of the first and second tubes, thecovered stent, and the mandrel on a rack in a heated oven;

FIG. 75 shows a microscopic view of the smooth covered stent;

FIG. 76 shows a microscopic view of the smooth covered stent;

FIG. 77 shows a perspective view of a tapered rod, a first hollowmandrel, a second hollow mandrel, and a stent;

FIG. 78 shows a perspective view of positioning the stent on the taperedrod of FIG. 77;

FIG. 79 shows a perspective view of positioning the tapered end of thetapered rod into the first hollow mandrel of FIG. 77;

FIG. 80 shows a perspective view of the first hollow mandrel positionedover the tapered end of the tapered rod of FIG. 77;

FIG. 81 shows a perspective view of sliding the stent along the taperedrod onto the first hollow mandrel of FIG. 77;

FIG. 82 shows a perspective of positioning the second hollow mandrelover the over an end of the first hollow mandrel of FIG. 77;

FIG. 83 shows a perspective view of the second hollow mandrel positionedover the end of the first hollow mandrel of FIG. 77 and sliding thestent along the first hollow mandrel onto the second hollow mandrel;

FIG. 84 shows a perspective view of the stent positioned on the secondhollow mandrel of FIG. 77;

FIG. 85 shows a perspective view of providing a mandrel with a firstlayer of elastomeric tube and an inner covering;

FIG. 86 shows a perspective view of the mandrel with the first layer ofelastomeric tube and inner covering positioned within the second hollowmandrel of FIG. 77;

FIG. 87 shows a perspective view of removing the second hollow mandrelfrom beneath the stent to allow the stent to position onto the innercovering, elastomeric tube, and mandrel;

FIG. 88 shows a perspective view of removing the mandrel from beneaththe first layer of elastomeric tube;

FIG. 89 shows a perspective view of positioning a support mandrel withholes beneath the first layer of elastomeric tube, positioning the outercovering over the stent to form the covered stent, and positioning thesecond layer of elastomeric tube over the outer covering;

FIG. 90 shows a transparent perspective view of the support mandrel withholes, the first and second layers of elastomeric tube, and the coveredstent;

FIG. 91 shows a transparent perspective view of the support mandrel withholes, the first and second layers of elastomeric tube, and the coveredstent and a perspective view of connecting a barb fitting with a cap tofirst ends of the first and second layers of elastomeric tubes and atubing line via a barb fitting to second ends of the first and secondlayers of elastomeric tubes;

FIG. 92 shows a perspective view of positioning the support mandrel withholes, the first and second layers of elastomeric tubes, and the coveredstent connected to the tubing line into a press fixture;

FIG. 93 shows a perspective view of the press fixture of FIG. 92 in aclosed position; and

FIG. 94 shows a perspective view of a smooth covered stent.

DETAILED DESCRIPTION OF THE DRAWINGS AND THE PREFERRED EMBODIMENTS

In the following detailed description of the various embodiments ofmethods of making a stent with a smooth covering, like elements andstructures are numbered or labeled alike.

Tube Expander with Press Fixture and Heated Press

FIGS. 1-25 illustrate an exemplary method of making a stent 100 with asmooth, uninterrupted covering. The stent 100 has a circularcross-section when expanded with an inner diameter 102, an outerdiameter 104, a first end 106, a second end 108, a longitudinal length110, an inner surface 112, an outer surface 114, and a plurality ofstruts 115.

The inner and outer diameters 102, 104 of the stent 100 may vary and aremeasured in the expanded state of the stent 100. For example, theexpanded inner diameter 102 may range from 5.0 to 14.0 mm, and in someexamples may range from 6.0 to 8.0 mm. When the stent 100 is used inaortic or venous indications, the expanded inner diameter 102 may range5.0 to 40 mm. The nominal diameter of the stent 100 is defined as theunrestrained diameter of a stent 100 in its expanded form. Forballoon-expandable stents, the diameter of the stent 100 is defined bythe expanded inner diameter 102 of the stent 100, and the stent 100 inits nominal diameter state may be expanded into the intended vessel sizeto resist compression. For self-expanding stents, the diameter of thestent 100 is defined by the expanded outer diameter 104 of the stent100, and the stent 100 will be oversized as compared to the intendedvessel to ensure constant outward force against the vessel. Thelongitudinal length 110 of the stent 100 is defined from the first end106 to the second end 108 of the stent 100 and will vary depending onthe intended vessel for implantation. In one example, the longitudinallength 110 of the stent 100 is 120 mm. When the stent 100 is used inaortic or venous indications, the longitudinal length 110 of the stent100 may be up to 300 mm.

A tube of elastomeric material 116 provides compression to the stent 100during an encapsulation process. The elastomeric tube 116 is hollow andincludes an inner diameter 118, an outer diameter 120, a first end 122,a second end 124, and a longitudinal length 126. The longitudinal length126 is defined from the first end 122 to the second end 124 of theelastomeric tube 116. The inner diameter 118 of the elastomeric tube 116may range from 2 mm to 15 mm. The outer diameter 120 of the elastomerictube 116 may range from 3 mm to 21 mm.

Suitable materials for the elastomeric material of the tube 116 includesilicone, neoprene, latex, butyl rubber, isoprene rubber, naturalrubber, Thoralon® or other thermosets, or other known or discoveredmaterials so long as they have the necessary properties described here.

Elastomeric materials are used because they have the capability ofresuming their original shape after deformation. Elastomeric materialsthat have high temperature stability and thus can withstand hightemperatures without melting are preferred. For example, silicone hasthe properties, among others, of high temperature stability, lowvolatile content, being capable of varying its hardness or softness, andchemical inertness that make it useful. The inventors have discoveredthat not all elastomeric tubes may be used in the methods here. Theinventors have discovered that advantageously the tubes they designedhaving very low durometer are preferred. In one example, the elastomerictube 116 includes a specifically designed low durometer silicone, suchas MED-4014, MED-4020, or MED-4025 sold by NuSil Technology or other lowdurometer silicone, such as custom blends of raw silicone, that providesimilar mechanical properties. On the shore hardness scale, thedurometer of the silicone may range from 10 Shore 00 to 30 Shore A,preferably approximately 15 to 25 Shore A, and preferably 20 Shore A.Depending on the type of low durometer silicone used, the tensilestrength may range from approximately 700 psi (4.8 MPa) to 1,400 psi(9.7 MPa), the tear strength is 130 ppi (22.9 kN/m) to 190 ppi (33.5kN/m), the specific gravity is 1.08 to 1.11, the elongation is 890% to1,330%, and stress at 200% strain of 40 psi (0.38 MPa) to 105 psi (0.72MPa).

Another important feature the inventors have discovered is theapplication of a coating to the inner surface of the elastomeric tube116. This reduces or eliminates tackiness of the elastomer to which thecoating is applied. For example, the coating may include MED-6670 soldby NuSil Technology, MED-6671 sold by NuSil Technology, or a similarfriction reducing coating for silicone surfaces. The coating helps toremove the stickiness of the elastomeric tube 116. The coating mayinclude a thickness ranging from 20 to 100 micrometers (μm), orpreferably a range of 40 to 50 micrometers (μm). In some examples, thecoating may have a higher durometer than the elastomeric tube. In otherexamples, the durometers may be close or the same. The coating is curedafter applying it to the elastomeric tube 116.

In the present method, to radially expand the elastomeric tube 116, theelastomeric tube 116 is positioned within a tube expander 128. FIG. 1shows a perspective view of the tube expander 128 that includes anopening 130 to receive a port 132. As shown in FIGS. 1, 3 and 4, theport 132 may be positioned within and sealed to the opening 130 of thetube expander 128. The port 132 is configured to receive differentsources or inputs, including a vacuum, a syringe, a pressure source, aheat source or other sources.

The tube expander 128 is hollow and includes a shape to conform to thetube and the device. Here it is shown having circular shape with aninner diameter 134, an outer diameter 136, a first end 138, a second end140, and a longitudinal length 142. The longitudinal length 142 isdefined from the first end 138 to the second end 140 of the tubeexpander 128. The elastomeric tube 116 is positioned through the firstand second ends 138, 140 of the tube expander 128. In its originalstate, the elastomeric tube 116 includes an outer diameter 120 smallerthan the inner diameter 134 of the tube expander 128. FIG. 2 shows across-sectional view of the elastomeric tube 116 within the tubeexpander 128.

After positioning the elastomeric tube 116 in the tube expander 128, thefirst and second ends 122, 124 of the elastomeric tube 116 may be rolledup over the first and second ends 138, 140 of the tube expander 128 tocreate a seal as shown in FIG. 3. The sealing of the elastomeric tube116 to the tube expander 128 helps to keep the elastomeric tube 116 inposition within the tube expander 128. Other sealing devices ortechniques or devices to maintain the position of the elastomeric tube116 within the tube expander 128 may be used. For example, devices suchas rings, sleeves, ties, caps, or other clamping devices may also bepositioned over the first and second ends 122, 124 of the elastomerictube 116 and the first and second ends 138, 140 of the tube expander 128to maintain the position of the elastomeric tube 116 within the tubeexpander 128 and to prevent the elastomeric tube 116 from moving alongthe longitudinal length 142 of the tube expander 128.

FIGS. 5A and 5B show rings 144 and caps 146, respectively, positionedover the first and second ends 122, 124 of the elastomeric tube 116 andthe first and second ends 138, 140 of the tube expander 128. FIGS. 2 and4 show cross-sectional views of the elastomeric tube 116 within the tubeexpander 128 before any source or input is applied to the tube expander128.

To radially expand the inner and outer diameters 118, 120 of theelastomeric tube 116, a vacuum may be applied to the tube expander 128.FIG. 5 shows a perspective view of connecting a vacuum source 148 to theport 132 of the tube expander 128. The vacuum source 148 is applied tothe tube expander 128 to uniformly expand the inner and outer diameters118, 120 of the elastomeric tube 116. When the vacuum source 148 isapplied, as described previously, the outer diameter 120 of theelastomeric tube 116 seals to the inner diameter 134 of the tubeexpander 128. This sealing of the elastomeric tube 116 to the tubeexpander 128 helps to prevent the elastomeric tube 116 from moving alongthe longitudinal length 142 of the tube expander 128. As shown in FIGS.6 and 7, when the vacuum source 148 is applied, the outer diameter 120of the elastomeric tube 116 is in contact with the inner diameter 134 ofthe tube expander 128.

A mandrel 150 is provided to support the stent 100 or other prosthesisand maintain the nominal diameter of the stent 100 or prosthesis duringthe covering or encapsulation process. FIG. 8 shows a perspective viewof the mandrel 150 that includes a diameter 152, a first end 154, asecond end 156, and a longitudinal length 158, which is defined as thelength from the first end 154 to the second end 156. The mandrel 150 maybe hollow or solid depending on the strength of the material of themandrel 150 and the heating characteristics or capabilities of themandrel 150. In some examples, the mandrel 150 may be hollow with aninner diameter 160. When the mandrel 150 is hollow, it may also includea plurality of holes 162. When the mandrel 150 is hollow, heat may beapplied internally within the mandrel 150, such as with a cartridgeheater, for allow for faster heating. A hollow mandrel 150 also allowsfor faster cooling. The material of the mandrel 150 may include glass,metal, stainless steel and/or an alloy. When the mandrel is solid, thediameter 152 of the mandrel 150 is smaller than the inner diameter 118of the elastomeric tube 116 in its expanded state.

An inner covering 164 is provided that is positioned over and wrappedaround the mandrel 150 as shown in FIG. 10A. In this example, the innercovering 164 includes a layer 164A of first material 166 and secondmaterial 168 that is used for covering the inner surface 112 of thestent 100 or a prosthesis. In an alternative example, the layer 164A ofthe inner covering 164 only includes the first material 166.

The dimensions of the inner covering 164 will vary depending on theinner diameter 102 and the longitudinal length 110 of the stent 100. Forexample, the inner covering 164 includes a rectangular or square crosssection with a width and a length. The length of the inner covering 64is the length of the inner covering 164 that wraps around the mandrel150. The width of the inner covering 164 is the length of the innercovering 164 that extends along the longitudinal length 158 of themandrel 150. In some examples, the width of the inner covering 164 mayrange from 1.25 to 6 inches.

The diameter 152 of the mandrel 150 and the inner and outer diameters118, 120 of the elastomeric tube 116 will also vary depending on theinner and outer diameters 102, 104 of the stent 100. In one example, thediameter 152 of the mandrel 150 is 6.0 mm and the inner diameter 118 ofthe elastomeric tube 116 is 6.0 mm. In particular, the inner diameter118 of the elastomeric tube 116 in its original state will varydepending on the outer diameter 104 of the stent 100.

The first material 166 and the second material 168 of the inner covering164 are parallel to each other within the layer 164A. The inner covering164 is positioned and wrapped around the mandrel 150 such that when thestent 100 is positioned over the inner covering 164 and the mandrel 150,the inner surface 112 of the stent 100 is completely covered with theinner covering 164. The inner covering 164 is positioned over themandrel 150 such that the first material 166 is in contact with themandrel 150 and the second material 168 is not in contact with themandrel 150. The second material 168 of the inner covering 164 contactsthe inner surface 112 of the stent 100 when the stent 100 is positionedover the inner covering 164.

The first material 166 preferably is a thermoplastic or a thermosetmaterial, such as polytetrafluoroethylene (PTFE), including electrospunPTFE (esPTFE) and expanded PTFE (ePTFE), electrospun polymers, and otherwoven or non-woven polymers. The second material 168 preferably is athermoplastic material, such as polyurethane, nylon, polyolefins,elastomers, fluorinate ethylene propylene (FEP), styrenic blockcopolymers (TPE-s), incluing SEBS, SIBS, SEBS, SEPS, SIS, polyolefinblends (TPE-o), elastomeric alloys (TPE-c or TPV), thermoplasticpolyurethanes (TPU), thermoplastic copolyester, and thermoplasticpolyamides. Electrospun materials and methods are disclosed in thefollowing patents and patent applications and are incorporated herein byreference: U.S. Pat. No. 9,060,852; 8,876,849; 8,795,577; 8,637,109;8,403,979; 8,211,168; 8,100,683; 7,779,261; 7,678,144; 7,641,844; U.S.Pub. No. 2015-0112383; U.S. Pub. No. 2014-0188212; U.S. Pub. No.2014-0081386; U.S. Pub. No. 2013-0122248; U.S. Pub. No. 2013-0018220;U.S. Pub. No. 2012-0259170; U.S. Pub. No. 2012-0141656; U.S. Pub. No.2011-0054512; U.S. Pub. No. 2010-0323052; U.S. Pub. No. 2009-0142505;U.S. Pub. No. 2008-0157444.

The inner covering 164 may include a second layer 164B of both the firstmaterial 166 and the second material 168. The inner covering 164 mayinclude one to ten layers of the first material 166 and the secondmaterial 168. When more than one layer is used, the layers arepositioned over the first layer 164A such that the first and secondmaterials 166, 168 maintain an alternating pattern. For example, thefirst material 166 of the second layer 164B contacts the second material168 of the first layer 164A, and the second material 168 of the secondlayer 164B does not contact either the first material 166 or the secondmaterial 168 of the first layer 164A.

The inner covering 164 may be rolled in a sterilized liquid, forexample, 70% or 100% isopropanol, ethanol, processed deionized water, orpropylene glycol, to assist the inner covering 164 to lay flat againstthe mandrel 150. Other sterilized liquids may also be used. To keep theinner covering 164 in place, a soldering iron may be used to tack orotherwise adhere edges of the inner covering 164 to the mandrel 150.Other types of adhesion or soldering devices, such as soldering guns andtips, may be used to adhere edges of the inner covering 164. Forexample, in one example, a soldering station, such as one sold byWeller, may be used with a blunt chisel tip.

The second material 168 may be referred to as a tie layer, a bondinglayer or an adhesive because it helps to bond the first material 166 ineach of the layers of the inner cover 164 together. The second material168 may have a lower melting point than the first material 166 to meltand flow through the porous structure of the first material 166 tocreate a bond between the first materials 166 of the layers 164A, 164Bof the inner covering 164. After the inner covering 164 is applied tothe mandrel 150, the mandrel 150 and the inner covering 164 include adiameter 170.

In this example, the stent 100 includes a balloon expandable stent. Aself-expanding stent may also be used, but a balloon-expanded stent maybe preferred in this example. A variety of biocompatible materials maybe used to construct the stent, including metals, and/or alloys,medically-acceptable polymers and/or bioabsorbable polymers ormaterials. For example, the metals and/or alloys may include stainlesssteel, tantalum, nitinol, tungsten, platinum, inconel, cobalt-chromiumalloys, iridium, molybdenum, moly-rhenium, other alloys of nitinol(including ternary and quaternary alloys), and magnesium or its alloys(as degradable stents). If a self-expanding stent it used, other stepsmay be required to prevent the diameter restriction of the stent 100,including pre-expansion of the stent 100 and cooling of the stent 100 toallow it to be positioned over the inner covering 164.

The inner diameter 102 of the stent 100 is greater than the diameter 170of the mandrel 150 and the inner covering 164 such that the stent 100may slide over the mandrel 150 and the inner covering 164. As shown inFIG. 10A, the stent 100 is positioned over the inner covering 164 andthe mandrel 150 and is in contact with the second material 168 of theinner covering 164. A crimper, such as an iris crimper, or otherreducing device may be used to uniformly secure the stent 100 in placeover the inner covering 164 and the mandrel 150. The stent 100 isapproximately at its nominal diameter when positioned over the mandrel150 and the inner covering 164, as well as after use of the crimper.

After the stent 100 is positioned over the inner covering 164 and themandrel 150, in this example, an outer covering 172 is provided thatincludes a layer 172A of the first material 166 and the second material168 that are parallel to each other within the layer 172A. In analternative example, the layer 172A of the outer covering 172 onlyincludes the first material 166. The outer covering 172 may bepositioned over and wrapped around the stent 100 such that the secondmaterial 168 of the outer covering 172 is in contact with the stent 100and the first material 166 is not in contact with the stent 100. Theouter covering 172 is positioned over and wrapped around the stent 100such that the outer surface 114 of the stent 100 is completely coveredwith the outer covering 172.

As with the inner covering 164, the outer covering 172 may include asecond layer 172B of both the first material 166 and the second material168. The outer covering 172 may include one to ten layers of the firstmaterial 166 and the second material 168. When more than one layer isused, the layers are positioned over the first layer 172A such that thefirst and second materials 166, 168 maintain an alternating pattern asdescribed previously with the inner covering 164. For example, thesecond material 168 of the second layer 172B contacts the first material166 of the first layer 172A, and the first material 166 of the secondlayer 172B does not contact either the first material 166 or the secondmaterial 168 of the first layer 172A.

As described previously with the inner covering 164, the outer covering172 may be rolled in a sterilized liquid, for example, 70% or 100%isopropanol, ethanol, processed deionized water, or propylene glycol, toassist the outer covering 172 to lay flat against the stent 100. Othersterilized liquids may also be used. Also, other types of adhesion orsoldering devices, such as soldering guns and tips, may be used toadhere edges of the outer covering 172.

After the outer covering 172 is applied to the stent 100, the innersurface 112 of the stent 100 is covered with the inner covering 164 andthe outer surface 114 of the stent 100 is covered with the outercovering 172, resulting in covered stent 174. The covered stent 174 andthe mandrel 150 include a diameter 176. The inner diameter 128 of theelastomeric tube 116 is smaller than or the same as the diameter 176.

The covered stent 174 and the mandrel 150 are then positioned within thelumen of the expanded elastomeric tube 116 in the tube expander 128 suchthat the elastomeric tube 116 covers the covered stent 174 as shown inFIGS. 8 and 9. For example, the longitudinal length 126 of theelastomeric tube 116 is greater than or the same as the longitudinallength 110 of the stent 100. FIGS. 10 and 10A show cross-sectional viewsof the elastomeric tube 116, the covered stent 174, and the mandrel 150within the tube expander 128 when the elastomeric tube 116 is in itsexpanded state. Once the mandrel 150 is in position, as shown in FIG.11, the vacuum source 148 may be released so that the elastomeric tube116 recovers to the covered stent 174 and surrounds the covered stent174. FIGS. 12 and 12A show cross-sectional views of the elastomeric tube116, the covered stent 174, and the mandrel 150 in the tube expander 128after the release of the vacuum source 148. After the release of thevacuum source 148, the outer diameter 120 of the elastomeric tube 116 issmaller than the inner diameter 134 of the tube expander 128.

After the vacuum source is released allowing the elastomeric tube 116 torecover to the covered stent 174, the elastomeric tube 116, the coveredstent 174, and the mandrel 150 are removed from the tube expander 128 asshown in FIG. 13. The elastomeric tube 116, the covered stent 174, andthe mandrel 150 together include a diameter 178. FIG. 14 shows across-sectional view of the mandrel 150, the covered stent 174, and theelastomeric tube 116 after removal from the tube expander 128. Pressureand heat are then applied to uniformly encapsulate and compress theinner and outer coverings 164, 172 and the stent 100 together.

In one example, after removal of the mandrel 150, the covered stent 174,and the elastomeric tube 166 from the tube expander 128 and prior toapplying pressure and heat, the mandrel 150, the covered stent 174, andthe elastomeric tube 166 may be placed in a vacuum chamber for apretreatment vacuum step. The pretreatment vacuum step may remove anyair bubbles from the elastomeric tube 166. Air bubbles within theelastomeric tube 166 may affect heating and bonding of the inner andouter coverings 164, 172 to the stent 100. The vacuum chamber may be anyvacuum chamber known in the art, and the mandrel 150 may be positionedon a rack in the vacuum chamber to provide uniform distribution of thepressure around the elastomeric tube 166. In one example, the vacuumpressure applied may be approximately 500 to 700 mmHg (vacuum pressure)may be applied for approximately 15 minutes to two (2) hours. In anotherexample, the vacuum pressure applied may be approximately 600 mmHg(absolute vacuum pressure) for approximately 1 hour. The vacuum pressureapplied may vary and may range from approximately 50 mmHg to 760 mmHg(absolute vacuum pressure), and as the vacuum pressure appliedincreases, the time the vacuum pressure will be applied decreases.

To apply pressure and heat to uniformly encapsulate and compress theinner and outer coverings 164,172 and the stent 100 together, in oneexample, as shown in FIG. 15A, a sleeve or cap 180 that is hollow andincludes an inner diameter 182 and an outer diameter 184 may bepositioned on each of the first and second ends 154, 156 of the mandrel150. The inner diameter 182 of the sleeve 180 is the same or slightlylarger than the diameter 152 of the mandrel 150 such that the sleeves180 may slide along the mandrel 150 to contact the first and second ends122, 124 of the elastomeric tube 116. The sleeves 180 help to prevent orminimize the longitudinal length 126 of the elastomeric tube 116 fromexpanding when pressure, heat and/or compression are applied and helpwith heat transfer. The sleeves 180 may include metal and/or alloys.

To apply pressure and heat, in one example as shown in FIG. 15, themandrel 150 with the covered stent 174, and the elastomeric tube 116 arepositioned in a press fixture 186. The press fixture 186 includes afirst portion 188 and a second portion 190. The first and secondportions 188, 190 each include a slot 192 for receiving the mandrel 150with the covered stent 174, and the elastomeric tube 116. The slots 192each include a half circular cross-section such that when the first andsecond portions 188, 190 connect, or the press fixture is closed, theslots 192 form a hollow circle with a diameter 194. The diameter 194 isthe same as or smaller than the diameter 178 of the mandrel 150, thecovered stent 174, and the elastomeric tube 116 together. In otherwords, the diameter 178 is the same or slightly larger than the diameter194 of the press fixture 186. Preferably, the diameter 178 is slightlylarger than the diameter 194 of the press fixture 186 such that thefirst and second portions 188, 190 of the press fixture 186 do notcontact each other when brought together until compression is applied tothe press fixture 186. The press fixture 186 may include multiple slots192 with varying diameters 194.

As shown in FIGS. 16 and 17, after positioning the mandrel 150 with thecovered stent 174 and the elastomeric tube 116 in one of the slots 192of the press fixture 186, the first and second portions 188, 190 arebrought together. The press fixture 186 is not completely closed whenthe first and second portions 188, 190 are brought together because thediameter 178 is larger than the diameter 194 of the slots 192 of thepress fixture 186. Thus, the first and second portions 188, 190 may notcontact each other until compression is applied to the press fixture186. FIGS. 17 and 17A show cross-sectional views of the mandrel 150, thecovered stent 174, and the elastomeric tube 116 within the press fixture186 before compression is applied.

As shown in FIG. 18, the press fixture 186 with the mandrel 150, thecovered stent 174, and the elastomeric tube 116 are then positioned in aheated press 196, such as those sold by Carver, Inc., to uniformly applycompression and heat to the elastomeric tube 116 and the covered stent174. When pressure is applied to the heated press 196, the pressurecompresses the press fixture 196, which compresses the elastomeric tube116 uniformly against the covered stent 174 and displaces theelastomeric tube 116 to ensure contact between the inner and outercoverings 164, 172 as shown in FIG. 19A. Heat is also applied to thepress fixture 186 to uniformly melt the second material 168 of the innerand outer coverings 164, 172 to bond the first material 166 of the innerand outer coverings 164, 172 together around the struts 115 of the stent100.

The amount of pressure applied may also vary, and in one example, isapplied until a pressure gauge on the heated press 196 moves slightly oruntil the first and second portions 188, 190 contact each other. Theamount of pressure applied depends on the size and durometer of theelastomeric tube 116, as more pressure will need to be applied tothicker and higher durometer elastomeric tubes 116. For example, ratherthan measuring the amount of pressure, the displacement of the thicknessof the elastomeric tube 116 may be measured. The displacement of thethickness of the elastomeric tube 116 allows the elastomeric tube 116 toconform around struts 115 of the stent 100. The displacement may rangefrom approximately 0.002 to 0.050 inches, and preferably will range fromapproximately 0.005 to 0.010 inches.

The amount of heat applied may vary depending on the material of thesecond material 168. For example, when the second material 168 ispolyurethane, the heat temperature may range from 380±5 to 430±5 degreesFahrenheit, and preferably is 390±5 degrees Fahrenheit. When the secondmaterial 168 is fluorinated ethylene propylene (FEP), the heattemperature may range from 490±5 to 540±5 degrees Fahrenheit, andpreferably is 500±5 degrees Fahrenheit. The amount of heat appliedshould be sufficient to melt the second material 168 of the inner andouter coverings 164, 172 and will vary depending on the type of secondmaterial 168 used. When the inner and outer coverings 164, 172 onlyinclude the first material 166, the inner and outer coverings 164, 172are heated to above the glass transition temperature of the firstmaterial 166.

The pressure applied minimizes the diameter 178 of the mandrel 150 withthe covered stent 174, and the elastomeric tube 116 together to be thesame as the diameter 194 of the slots 192 of the press fixture 186 andcompresses the elastomeric tube 116 against the covered stent 174 in auniform distribution around the elastomeric tube 116. The pressure andheat may be applied for a time of one minute. However, the time that thepressure and heat are applied may increase or decrease depending on theamount of pressure and heat necessary to displace the thickness of theelastomeric tube 116 to conform around the struts 115 of the stent 100and melt the second material 168 of the inner and outer coverings 164,172.

Alternatively, pressure may be applied to the press fixture 186 bycompression molding or an alternative pressure source that would permiteven pressure distribution around the elastomeric tube 116 and thecovered stent 174. Also, heat may also be applied through the mandrel150, such as described previously with a cartridge heater, if themandrel 150 is hollow, to heat the covered stent 174 to melt the secondmaterial 168 of the inner and outer coverings 164, 172.

The application of heat and pressure to the covered stent 174 uniformlyencapsulates the stent 100 with the inner and outer coverings 164, 172to form a smooth covered stent 198. The smooth covered stent 198includes no visible creases, and the inner and outer coverings 164, 172include no creases or ridges that create distortions or lack ofcontinuity on the inner and outer coverings 164, 172. The press fixture196 and the elastomeric tube 116 permit uniform pressure and heatdistribution around the covered stent 174. FIG. 19A shows across-sectional view of the mandrel 150, the smooth covered stent 198,and the elastomeric tube 116 after the heat and pressure are applied fora specific time. After the heat and pressure are applied, the pressfixture 186 is removed from the heated press 196 and the elastomerictube 116, the smooth covered stent 198, and the mandrel 150 are removedfrom the press fixture 186. The elastomeric tube 116, the smooth coveredstent 198, and the mandrel 150 may be placed in room temperature waterto cool, blown with compressed air to cool, allowed to cool to roomtemperature of the air, or cooled with freeze spray or liquid nitrogen.

In one example, the elastomeric tube 116 may be removed from the smoothcovered stent 198 by positioning the elastomeric tube 116, the smoothcovered stent 198, and the mandrel 150 through the tube expander 128.The first and second ends 122, 124 of the elastomeric tube 116 may berolled up over the first and second ends 138, 140 of the tube expander128 to create a seal. As discussed above, sealing devices or techniquesto maintain the position of the elastomeric tube 116 within the tubeexpander 128 may be used.

The vacuum source 148 is applied to the tube expander 128 to uniformlyexpand the inner and outer diameters 118, 120 of the elastomeric tube116. The vacuum source 128 causes the inner and outer diameters 118, 120of the elastomeric tube 116 to uniformly expand so that the outerdiameter 120 of the elastomeric tube 116 is in contact with the innerdiameter 134 of the tube expander 128. The smooth covered stent 198 andthe mandrel 150 are removed from the tube expander 128, and the vacuumsource 148 is released to allow the elastomeric tube 116 to recover. Themandrel 150 is then removed from the smooth covered stent 198 as shownin FIGS. 23 and 24. FIGS. 75 and 76 show microscopic views of the smoothcovered stent 198, and the outer covering 172 conforming around strutsof the stent 100.

During the encapsulation process, the inner and outer diameters 102, 104of the stent 100 remain approximately the same to maintain integrity ofthe stent 100. Thus, from the beginning of the encapsulation process,when the stent 100 is positioned over the inner covering 164, until theend of the encapsulation process, when the smooth covered stent 198 isformed, the stent 100 maintains its nominal diameter.

In an alternative example, if a self-expanding stent is used, a secondelastomeric tube may be positioned around the mandrel 150 via the tubeexpander 128 including the vacuum 148, as described previously above,prior to placement of the inner covering 164 over the mandrel 150. Afterplacement of the second elastomeric tube around the mandrel 150, tensionis applied to the second elastomeric tube to radially decrease the outerdiameter of the second elastomeric tube to allow the stent 100 to slideor otherwise be positioned over the second elastomeric tube on themandrel 150. Specifically, the tension applied outer diameter of thesecond elastomeric tube is less than the inner diameter 102 of the stent100. The tension may be applied by using clamps to pull on the ends ofthe second elastomeric tube. With the tension applied to the secondelastomeric tube on the mandrel 150, the inner covering 164 ispositioned over and wrapped around the second elastomeric tube with thefirst material 166 of the inner covering 164 in contact with the secondelastomeric tube, as described previously. The stent 100 is positionedover the inner covering 164 and in contact with the second material 168of the inner covering 164. After the stent 100 is positioned over theinner covering 164, the tension applied to the second elastomeric tubemay be released and the clamps removed. When the tension is released,the second elastomeric tube radially expands to a non-tension appliedstate. After expansion, the inner covering 164 contacts the innerdiameter 102 of the stent 100, and the stent 100 maintains its nominaldiameter and is not significantly expanded. The subsequent stepsdescribed above to form the smooth covered stent 198 may then beapplied, including without limitation the application of an outercovering 172, the application of the elastomeric tube 116, and theapplication of heat and pressure using a press fixture 186 and heatedpress 196.

The tables and steps below provide examples of the materials and stepsusing the aforementioned method.

EXAMPLE 1 Balloon-Expandable Stent and Inner and Outer Coveringsincluding First and Second Materials

Element Specifications Stent 100 Inner diameter 102 is 6.0 mm, outerdiameter 104 is 6.4 mm, nominal diameter is 6 mm, longitudinal length110 is 30 mm, balloon-expandable Elastomeric tube inner diameter 118 is6 mm, outer diameter 120 is 116 8 mm, longitudinal length 126 is 75 mm,and the material is silicone with a durometer of 20-25 Shore A CoatingMED-6670, thickness is 45 μm Tube expander 128 inner diameter 134 is 14mm Inner covering 164 includes first material 166 and second material168 First material 166 esPTFE Second material 168 polyurethane Outercovering 172 includes first material 166 and second material 168 Mandrel150 diameter is 6 mm, the material is glass with smooth finish Slot 192of Press diameter 194 of slot 192 is 8 mm Fixture 186

Steps:

-   -   The coating is applied to the inner diameter 118 of the        elastomeric tube 116 and then cured;    -   The elastomeric tube 116 is positioned within the tube expander        128 including the port 128 and the vacuum 148;    -   The mandrel 150 is provided;    -   The inner covering 164 is rolled in 70% isopropanol;    -   The inner covering 164 is positioned or wrapped around the        mandrel 150 with the first material 166 in contact with the        mandrel 150;    -   The stent 100 is initially slightly over-expanded and then        positioned over the inner covering 164 and in contact with the        second material 168 of the inner covering 164;    -   An Iris crimper is used to secure the stent 100 to the inner        covering 164;    -   The outer covering 172 is rolled in 70% isopropanol;    -   The outer covering 172 is positioned or wrapped around the stent        100 with the second material 168 of the outer covering 172 in        contact with the stent 100 to form the covered stent 174;    -   The first and second ends 122, 124 of the elastomeric tube 116        are rolled up and wrapped around the first and second ends 138,        140 of the tube expander 128;    -   The vacuum 148 is applied expanding the inner and outer        diameters 118, 120 of the elastomeric tube 116 until the outer        diameter 120 of the elastomeric tube 116 contacts the inner        diameter 134 of the tube expander 128;    -   The covered stent 174 and the mandrel 150 are positioned in the        tube expander 128;    -   The vacuum 148 is released allowing the inner and outer        diameters 118, 120 of the elastomeric tube 116 to retract to an        unexpanded state and recover to the covered stent 174;    -   The elastomeric tube 116, the covered stent 174, and the mandrel        150 are positioned in a vacuum chamber with an applied pressure        of 600 mmHg (absolute vacuum pressure) for 1 hour;    -   The elastomeric tube 116, the covered stent 174, and the mandrel        150 are removed from the vacuum chamber and positioned in the        slot 192 of the press fixture 186 and the first and second        portions 188, 190 of the press fixture 186 are brought together;    -   The press fixture 186 is positioned in the heated press 196;    -   Pressure is applied to the press fixture 186 to displace the        thickness of elastomeric tube 116 by 0.005±0.001 inches;    -   Heat is applied to the press fixture 186 to 390±5 degrees        Fahrenheit and is applied for 1 minute time;    -   The press fixture 186 is removed from the heated press 196;    -   The elastomeric tube 116, the smooth covered stent 198, and the        mandrel 150 are removed from the press fixture 186 and        positioned in room temperature water for cooling;    -   The elastomeric tube 116, the smooth covered stent 198, and the        mandrel 150 are positioned in the tube expander 128;    -   The first and second ends 122, 124 of the elastomeric tube 116        are rolled up and wrapped around the first and second ends 138,        140 of the tube expander 128;    -   The vacuum 148 is applied allowing the inner and outer diameters        118, 120 of the elastomeric tube 116 to uniformly expand;    -   The smooth covered stent 198 and the mandrel 150 are removed        from the tube expander 128; and    -   The mandrel 150 is removed from the smooth covered stent 198.

EXAMPLE 2 Balloon-Expandable Stent and Inner and Outer Coveringsincluding First Material

Element Specifications Stent 100 Inner diameter 102 is 8.0 mm, outerdiameter 104 is 8.4 mm, nominal diameter is 8 mm, longitudinal length126 is 30 mm, balloon-expandable Elastomeric tube inner diameter 118 is8 mm, outer diameter 120 116 is 10 mm, longitudinal length 126 is 75 mm,and the material is silicone with a durometer of 20 Shore A CoatingMED-6670, thickness is 45 μm Tube expander 128 inner diameter 134 is 14mm Inner covering 164 includes first material 166 only First material166 esPET Outer covering 172 includes first material 166 only Mandrel150 diameter is 8 mm, the material is stainless steel Slot 192 of Pressdiameter 194 of slot 192 is 10 mm Fixture 186

Steps:

-   -   The coating is applied to the inner diameter 118 of the        elastomeric tube 116 and then cured;    -   The elastomeric tube 116 is positioned within the tube expander        128 including the vacuum 148;    -   The mandrel 150 is provided;    -   The inner covering 164 is rolled in 70% isopropanol;    -   The inner covering 164 is positioned or wrapped around the        mandrel 150;    -   The stent 100 is initially slightly over-expanded and then        positioned over the inner covering 164;    -   An Iris crimper is used to secure the stent 100 to the inner        covering 164;    -   The outer covering 172 is rolled in 70% isopropanol;    -   The outer covering 166 is positioned or wrapped around the stent        100 to form the covered stent 174;    -   The first and second ends 122, 124 of the elastomeric tube 116        are rolled up and wrapped around the first and second ends 138,        140 of the tube expander 128;    -   The vacuum 148 is applied expanding the inner and outer        diameters 118, 120 of the elastomeric tube 116 until the outer        diameter 120 of the elastomeric tube 116 contacts the inner        diameter 134 of the tube expander 128;    -   The covered stent 174 and the mandrel 150 are positioned in the        tube expander 128;    -   The vacuum 148 is released allowing the inner and outer        diameters 118, 120 of the elastomeric tube 116 to retract to an        unexpanded state and recover to the covered stent 174;    -   The elastomeric tube 116, the covered stent 174, and the mandrel        150 are positioned in a vacuum chamber with an applied pressure        of 600 mmHg (absolute vacuum pressure) for 1 hour;    -   The elastomeric tube 116, the covered stent 174, and the mandrel        150 are removed from the vacuum chamber and positioned in the        slot 192 of the press fixture 186 and the first and second        portions 188, 190 of the press fixture 186 are brought together;    -   The press fixture 186 is positioned in the heated press 196;    -   Pressure is applied to the press fixture 186 to displace the        thickness of elastomeric tube 116 by 0.005±0.001 inches;    -   Heat is applied to the press fixture 186 to 365±5 degrees        Fahrenheit and is applied for 1 minute time;    -   The press fixture 186 is removed from the heated press 196;    -   The elastomeric tube 116, the smooth covered stent 198, and the        mandrel 150 are removed from the press fixture 186 and        positioned in room temperature water for cooling;    -   The elastomeric tube 116, the smooth covered stent 198, and the        mandrel 150 are positioned in the tube expander 128;    -   The first and second ends 122, 124 of the elastomeric tube 116        are rolled up and wrapped around the first and second ends 138,        140 of the tube expander 128;    -   The vacuum 148 is applied allowing the inner and outer diameters        118, 120 of the elastomeric tube 116 to uniformly expand;    -   The smooth covered stent 198 and the mandrel 150 are removed        from the tube expander 128; and    -   The mandrel 150 is removed from the smooth covered stent 198.

Manual Removal of the Elastomeric Tube

In another example, as shown in FIG. 22, the elastomeric tube 116 may beremoved from the smooth covered stent 198 by ripping or peeling theelastomeric tube 116 away from the smooth covered stent 198. Theelastomeric tube 116 may also be removed by skiving or pulling theelastomeric tube 116 along a longitudinal length 200 of the smoothcovered stent 198. The mandrel 150 is removed from the smooth coveredstent 198 as shown in FIGS. 23 and 24. FIG. 25 shows a cross-sectionalview of the smooth covered stent 198. If the longitudinal length 200 ofthe smooth covered stent 198 exceeds beyond the desired length, anyexcess on a first end 202 and second end 204 of the smooth covered stent198 may be trimmed, cut, or otherwise removed.

Swelling Agent for Radial Expansion of Elastomeric Tube

Another example of expanding the inner and outer diameters 118, 120 ofthe elastomeric tube 116 includes placing the elastomeric tube 116 in acontainer including a swelling agent. The container may include a glassvial or any other container capable of holding a liquid. The swellingagent may include hexane, volatile methyl siloxane, Freon®, Swellex®,Swellex® P, or other swelling agents.

The elastomeric tube 116 remains in the container with the swellingagent until the elastomeric tube 116 is adequately expanded so that theinner diameter 118 of the elastomeric tube 116 is greater than thediameter 170 of the mandrel 150 and the covered stent 174. Thus, thetime the elastomeric tube 116 remains in the container with the swellingagent may vary, and may include approximately ten minutes.

The elastomeric tube 116 is then removed from the container, and themandrel 150 and the covered stent 174 may be positioned within theelastomeric tube 116 such that the elastomeric tube 116 surrounds thecovered stent 174. For example, the longitudinal length 126 of theelastomeric tube 116 is greater than or the same as the longitudinallength 110 of the stent 100. The elastomeric tube 116, the mandrel 150,and the covered stent 174 are allowed to air dry under a fume hood,exposed to a dryer, such as an electric dryer, or otherwise permitted todry to allow the elastomeric tube 116 to recover to the covered stent174. Heat and pressure are then applied to the covered stent 174 asdescribed previously including the press fixture 186 and the heatedpress 196 to uniformly form the smooth covered stent 198.

After the heat and pressure are applied, the press fixture 186 isremoved from the heated press 196, and the mandrel 150, the smoothcovered stent 198, and the elastomeric tube 116 are removed from thepress fixture 186. The elastomeric tube 116 may then be removed from thesmooth covered stent 198 by any of the methods previously describedincluding by ripping or peeling the elastomeric tube 116 away from thesmooth covered stent 198, by using the tube expander 128 to uniformlyexpand the inner and outer diameters 118, 120 of the elastomeric tube116 away from the smooth covered stent 198, or by placing elastomerictube 116, the smooth covered stent 198, and the mandrel 150 in thecontainer with the swelling agent to uniformly expand the inner andouter diameters 118, 120 of the elastomeric tube 116 away from thesmooth covered stent 198. After the elastomeric tube 116 is removed fromthe smooth covered stent 198, the mandrel 150 is then removed from thesmooth covered stent 198.

Expansion Mandrels and Slit Cannula

FIGS. 26-64 show another example of a method of making a stent with asmooth covering. A slit cannula 300 is provided that is hollow andincludes a circular cross section with an inner diameter 302, an outerdiameter 304, a first end 306, a second end 308, and a longitudinallength 310, which is defined from the first end 306 to the second end308 as shown in FIG. 26. The material of the slit cannula 300 ispolytetrafluoroethylene (PTFE), including Teflon®, stainless steel oranother material that is capable of withstanding the pressure andtemperature without material failure.

In this example, the stent 100 includes a self-expanding stent. However,a balloon-expandable stent may also be used. A variety of biocompatiblematerials may be used to construct the stent, including metals, and/oralloys, medically-acceptable polymers and/or bioabsorbable polymers ormaterials. For example, the metals and/or alloys may include stainlesssteel, tantalum, nitinol, tungsten, platinum, inconel, cobalt-chromiumalloys, iridium, molybdenum, moly-rhenium, other alloys of nitinol(including ternary and quaternary alloys), and magnesium or its alloys(as degradable stents).

The slit cannula 300 also includes a plurality of slits 312. The slits312 include a first end 314, a second end 316, and a longitudinal length318, which is defined from the first end 314 to the second end 316. Thelongitudinal length 318 of the slits 312 is smaller than thelongitudinal length 310 of the slit cannula 300. The slits 312 allowradial expansion of the slit cannula 300 and the inner and outerdiameters 302, 304 of the slit cannula 300 to increase.

In one example, as shown in FIGS. 26-32, the first ends 314 of the slits312 begin either at the first or second ends 306, 308 of the slitcannula 300. The second ends 316 of the slits 312 do not interact witheither the first or second ends 306, 308 of the slit cannula 300. Thesecond ends 316 of the slits 312 each include a circular end 320. Thecircular ends 320 provide stress relief and release on the slits 312during expansion of the slit cannula 300 and prevent the longitudinallength 318 of the slits 312 from increasing and thereby extending thesecond ends 316 of the slits 312 to either the first or second ends 306,308 of the slit cannula 300.

The slits 312 form an alternating pattern around the outer diameter 304of the slit cannula 300 such that if the first end 314 of one of theslits 312 begins at the first end 306 of the slit cannula 300, the firstend 314 of the adjacent slits 312 begins at the second end 308 of theslit cannula 300. For example, as shown in FIGS. 26-32, the slit cannula300 includes twelve slits 312. In other examples, 8 to 10 slits may beused depending on the outer diameter 104 of the stent 100. FIG. 27 showsa cross-sectional view of the first end 306 of the slit cannula 300, andFIG. 28 shows a cross-sectional view of the second end 308 of the slitcannula 300. The number of slits 312 will vary depending on the innerand outer diameters 302, 304 of the slit cannula 300.

The inner and outer diameters 302, 304 of the slit cannula 300 will varydepending on the nominal diameter of the stent 100. For example, thenominal diameter of the stent 100 may range from 5-14 mm. When the stent100 is used in aortic or venous indications, the expanded outer diameter104 may range 5.0 to 40 mm. The inner diameter 302 of the slit cannula300 may range from 2.16±0.13 to 5.33±0.13 mm, and the outer diameter 304may range from 3.175±0.13 to 6.35±0.13 mm.

In one example, as shown in FIGS. 30-32, a first mandrel 322 is providedas a support base for the slit cannula 300. The material of the firstmandrel 322 includes glass, metal, stainless steel or an alloy, andpreferably stainless steel. As shown in FIG. 32, when the first mandrel322 is fully inserted within the slit cannula 300, the portion of theslit cannula 300 covering the first mandrel 322 is expanded. The firstmandrel 322 includes a circular cross-section with a first portion 323and a second portion 325. The first portion 323 includes a diameter 324,and the second portion 325 includes a diameter 327. The diameter 324 ofthe first portion 323 is greater than the diameter 327 of the secondportion 325. In an alternative example, the first mandrel 322 may behollow to allow for faster heating and cooling or alternative methods ofheating and cooling underneath the stent 100.

The first mandrel 322 includes a first end 326, a second end 328, a tip330, and a longitudinal length 332, which is defined from the first end326 to the second end 328 of the first mandrel 322. The longitudinallength 332 of the first mandrel 322 is smaller than the longitudinallength 310 of the slit cannula 300. The tip 330 is located at the firstend 326 of the first mandrel 322. In an alternative example, the firstmandrel 322 may be permanently fixed with the slit cannula to providestability.

As shown in FIGS. 30-32, in one example, the first mandrel 322 includesa handle 334. The handle 334 has a circular cross section, a first end336, a second end 338, and a slot 340 that has a circular cross sectionfor receiving the second portion 325 of the first mandrel 322. Forexample, when the diameter 327 of the second portion 325 is 0.1250±0.005inches, the diameter of the slot 340 of the handle 334 is 0.1260±0.005inches. The handle 334 slides onto the second portion 325 and isattached to the first mandrel 322 by a press fit and/or other fasteningmeans that permit the handle 334 to be easily removed from the firstmandrel 322. In an alternative example, the first mandrel 322 does notinclude a handle 334. In another example, the second portion 325 of thefirst mandrel 322 is knurled or machined to allow for gripping orhandling of the first mandrel 322. The material of the handle 334includes glass, metal, stainless steel or an alloy, and preferablystainless steel.

A first layer of elastomeric tube 342 is provided and positioned over anon-expanded portion of the slit cannula 300 as shown in FIG. 33. Asdescribed previously, the elastomeric material of the tube 342 mayinclude the same material as the elastomeric tube 116 or, preferably, anelastomeric material with a higher durometer than the elastomeric tube116. The elastomeric tube 342 includes an inner diameter 344 , an outerdiameter 346, and a thickness 345, which is defined from the innerdiameter 344 to the outer diameter 346. In its original state, the innerdiameter 344 of the elastomeric tube 342 is slightly smaller than theouter diameter 304 of the slit cannula 300. The inner and outerdiameters 344, 346 will vary depending on the nominal diameter of thestent 100. For example, the nominal diameter of the stent 100 may rangefrom 5 to 14 mm. The outer diameter 346 may range from 0.130±0.005 to0.524±0.005 inches. The inner diameter 344 may range from 0.090±0.005 to0.484±0.005 inches. When the stent 100 is used in aortic or venousindications, the expanded outer diameter 102 may range 5.0 to 40 mm. Thefirst layer of elastomeric tube 342 is hollow and includes a first end348, a second end 350, and a longitudinal length 352. The longitudinallength 352 is defined from the first end 348 to the second end 350 ofthe elastomeric tube 342 and is the same as or slightly smaller than thelongitudinal length 310 of the slit cannula 300.

The inner covering 164 including the first material 166 and the secondmaterial 168, as described previously, that is used to cover the innersurface 112 of the stent 100 or a prosthesis, is positioned over andwrapped around the first layer of elastomeric tube 342 as shown in FIG.34. The first material 166 is in contact with the first layer of theelastomeric tube 342. The stent 100 is then positioned over the innercovering 164 and is in contact with the second material 168 of the innercovering 164.

As described previously, the inner covering 164 may include more thanone layer such that the first and second materials 166, 168 of the innercovering 164 to maintain an alternating pattern underneath the stent100. To keep the layers in place, as previously described, a solderingiron may be used to tack or otherwise adhere edges of the inner covering164. In other examples, the first mandrel 322 is provided after thefirst layer of elastomeric tube 342, the inner covering 164, and thestent 100 are positioned over the slit cannula 300.

A coating, as previously described, that reduces the friction on thesurface of the first layer of elastomeric tube 342 may be applied to theouter diameter 346 of the first layer elastomeric tube 342. The coatinghelps to remove the stickiness or tackiness of the first layer ofelastomeric tube 342, so that the first layer of elastomeric tube 342does not stick to the inner covering 164.

As shown in FIG. 35, a second mandrel 354 is provided to expand the slitcannula 300, the first layer of elastomeric tube 342, and the innercovering 164. The material of the second mandrel 354 includes glass,metal, stainless steel or an alloy, and preferably stainless steel.After expansion, the inner covering 164 contacts the inner diameter 102of the stent 100, and the stent 100 maintains its nominal diameter andis not significantly expanded.

The second mandrel 354 includes a circular cross-section with a firstportion 356 and a second portion 358. The first portion 356 includes adiameter 360, and the second portion 358 includes a diameter 362. Thediameter 360 of the first portion 356 is greater than the diameter 362of the second portion 358. The second mandrel 354 includes a first end364, a second end 366, a tip 368, and a longitudinal length 370, whichis defined from the first end 364 to the second end 366 of the secondmandrel 356. The longitudinal length 370 of the second mandrel 354 issmaller than the longitudinal length 310 of the slit cannula 300. Thetip 368 is located at the first end 364 of the second mandrel 354. In analternative example, the second mandrel 354 may be permanently fixedwith the slit cannula to provide stability. In an alternative example,the first mandrel 322 may be hollow to allow for faster heating andcooling or alternative methods of heating and cooling underneath thestent 100.

When the second mandrel 354 is fully inserted within the slit cannula300, the portion of the slit cannula 300 that covers the second mandrel354 and the stent 100 is expanded, and the tip 368 of the second mandrel354 is in contact with the tip 330 of the first mandrel 322. As shown inFIG. 36, the second mandrel 354 extends beneath the longitudinal length110 of the stent 100 so the first layer of elastomeric tube 342 and theinner covering 164 are expanded to contact the inner diameter 102 of thestent 100. The stent 100 is not expanded and maintains its nominaldiameter when the second mandrel 354 is fully inserted within the slitcannula 300.

The second mandrel 354 also includes a handle 372. The handle 372 has acircular cross section, a first end 374, a second end 376, and a slot378 that has a circular cross section for receiving the second portion358 of the second mandrel 354. For example, when the diameter 362 of thesecond portion 358 is 0.1250±0.005 inches, the diameter of the slot 378of the handle 372 is 0.1260±0.005 inches. The handle 372 slides onto thesecond portion 358 of the second mandrel 354 and is attached to thesecond mandrel 354 by a press fit and/or other fastening means thatpermit the handle 372 to be easily removed from the second mandrel 354.In an alternative example, the second mandrel 354 does not include ahandle 372. In another example, the second portion 358 of the secondmandrel 354 is knurled or machined to allow for gripping or handling ofthe second mandrel 354. The material of the handle 373 includes glass,metal, stainless steel or an alloy, and preferably stainless steel.

After expanding the slit cannula 300, the outer covering 172, includingthe first material 166 and the second material 168, as describedpreviously, that is used for encapsulating the stent 100 or aprosthesis, is positioned over and wrapped around the stent 100 as shownin FIG. 36. The second material 168 is in contact with the stent 100,and the first material 166 is not in contact with the stent 100. Asdescribed previously, additional layers may also be added such that thefirst and second materials 166, 168 of the layers maintain analternating pattern over the stent 100. To keep the layers in place, aspreviously described, a soldering iron may be used to tack or otherwiseadhere edges of the layers.

As shown in FIG. 38, a second layer of elastomeric tube 380 ispositioned in the tube expander 128. As described previously, theelastomeric material of the tube 380 may include the same material asthe elastomeric tube 116. The elastomeric tube 380 is hollow andincludes a circular cross section with an inner diameter 382, an outerdiameter 384, a first end 386, a second end 388, and a longitudinallength 390. The longitudinal length 390 is defined from the first end386 to the second end 388 of the elastomeric tube 380. The second layerof elastomeric tube 380 is positioned within the tube expander 128, aspreviously described, to uniformly expand the inner and outer diameters382, 384 of the elastomeric tube 380. As previously described, the firstand second ends 386, 388 of the elastomeric tube 380 may be may berolled up over the first and second ends 138, 140 of the tube expander128 to create a seal. The vacuum source 148 is applied to the tubeexpander 128 to uniformly expand the inner and outer diameters 382, 384of the elastomeric tube 380.

A coating, as previously described, that reduces the friction on thesurface of the second layer of elastomeric tube 380 may be applied tothe inner diameter 382 of the second layer elastomeric tube 380. Thecoating helps to remove the stickiness or tackiness of the second layerelastomeric tube 380, so that the second layer elastomeric tube 380 doesnot stick to the outer covering 172.

As shown in FIG. 37, one or both of the handles 334, 372 may be removedfrom the second portions 325, 358 of the first and second mandrels 322,354 in order to position the slit cannula 300 with the covered stent 174and the first and second mandrels 322, 354 within the tube expander 128.The slit cannula 300 and the covered stent 174 are positioned with thetube expander 128 as shown in FIG. 38, and then the vacuum source 148 isreleased to allow the inner and outer diameters 382, 384 of the secondlayer of elastomeric tube 380 to return to an unexpanded state andrecover to the covered stent 174. The second layer of elastomeric tube380 and the covered stent 174 are removed from the tube expander 128 asshown in FIG. 39, and the handles 334, 372 may then be positioned backon the first and second mandrels 322, 354.

In one example, as described previously, after removal from the tubeexpander 128 and prior to applying pressure and heat, the first andsecond layers of elastomeric tube 342, 380, the covered stent 174, theslit cannula 300, and the first and second mandrels 322, 354 may beplaced in a vacuum chamber for a pretreatment vacuum step. Thepretreatment vacuum step may remove any air bubbles from the first andsecond layers of elastomeric tube 342, 380. Air bubbles within the firstand second layers of elastomeric tube 342, 380 may affect heating andbonding of the inner and outer coverings 164, 172 to the stent 100. Thevacuum chamber may be any vacuum chamber known in the art, and the firstand second mandrels 322, 354 may be positioned on a rack in the vacuumchamber to provide uniform distribution of the pressure around the firstand second layers of elastomeric tube 342, 380. In one example, thevacuum pressure applied may be approximately 500 to 700 mmHg (vacuumpressure) may be applied for approximately 15 minutes to two (2) hours.In another example, the vacuum pressure applied may be approximately 600mmHg (absolute vacuum pressure) for approximately 1 hour. The vacuumpressure applied may vary and may range from approximately 50 mmHg to760 mmHg (absolute vacuum pressure), and as the vacuum pressure appliedincreases, the time the vacuum pressure will be applied decreases.

As shown in FIGS. 40-42, the first and second layers of elastomeric tube342, 380, the covered stent 174, the slit cannula 300, and the first andsecond mandrels 322, 354 are positioned in the press fixture 186 andthen in the heated press 196, where heat and pressure are applied aspreviously described to create the smooth covered stent 198.Alternatively, heat and pressure may be applied as described in the“First and Second Tubes with Heated Oven” example, or other heat andpressure applications.

The first and second layers of elastomeric tube 342, 380, the smoothcovered stent 198, the slit cannula 300, and the first and secondmandrels 322, 354 are cooled, and then the handles 334, 372 may beremoved from the first and second mandrels 322, 354 to position thesecond layer of elastomeric tube 380 and the smooth covered stent 198 inthe tube expander 128 to remove the second layer of elastomeric tube 380as shown in FIGS. 42-43. Other removal methods as described previouslymay also be used to remove the second layer of elastomeric tube 380 fromthe smooth covered stent 198. The handles 334, 372 are positioned backedon the first and second mandrels 322, 354 as shown in FIG. 44. As shownin FIG. 45, the second mandrel 354 is removed from the slit cannula 300,which decreases the outer diameter 304 of the slit cannula 300, and thenthe smooth covered stent 198 is removed from the slit cannula 300.

As shown in FIG. 46, the smooth covered stent 198 may include aplurality of stripes or indentations 392 on an inner surface 394 of thesmooth covered stent 198 from compression against the slits 312 of theslit cannula 300. When the material of the first layer of elastomerictube 342 includes an elastomeric material with a higher durometer thanthe material of the elastomeric tube 116, the stripes or indentations392 may not form or are reduced in frequency.

As shown in FIGS. 47-49, to remove the strips 392 and to smooth theinner surface 394 of the smooth covered stent 198, a mandrel 396 with adiameter 398 is provided. The mandrel 396 includes a smooth outersurface 400, which may include glass or other suitable material with asmooth outer surface. The mandrel 396 is positioned within the smoothcovered stent 198, and a first layer of elastomeric tube 402 with aninner diameter 404 and an outer diameter 406 is positioned over thesmooth covered stent 198. The first layer of elastomeric tube 402 mayinclude the same material as the elastomeric tube 116 previouslydescribed. The tube expander 128 may be used to uniformly expand thefirst layer of elastomeric tube 402 over the smooth covered stent 198. Acoating, as previously described, that reduces the friction on thesurface of the first layer of elastomeric tube 402 may be applied to theinner diameter 404 of the first layer of elastomeric tube 402 so thatthe first layer of elastomeric tube 402 does not stick to the smoothcovered stent 198.

As shown in FIG. 49, a second layer of elastomeric tube 408 with aninner diameter 410 and an outer diameter 412 is positioned over thefirst layer of elastomeric tube 402. The second layer of elastomerictube 408 may include the same material as the elastomeric tube 116previously described. The inner and outer diameters 410, 412 of thesecond layer of elastomeric tube 408 are smaller than the inner andouter diameters 404, 406 of the first layer of elastomeric tube 402. Toposition the second layer of elastomeric tube 408 over the first layerof elastomeric tube 402, the tube expander 128 may be used to uniformlyexpand the second layer of elastomeric tube 408 over the first layer ofelastomeric tube 402. A coating, as previously described, that reducesthe friction on the surface of the second layer of elastomeric tube 408may be applied to the inner diameter 410 of the second layer ofelastomeric tube 408 so that the second layer of elastomeric tube 408does not stick to the first layer of elastomeric tube 402.

The mandrel 396, the smooth covered stent 198, and the first and secondlayers of elastomeric tube 402, 408 are positioned in the press fixture186 and then in the heated press 196, where heat and pressure areapplied as previously described and as shown in FIGS. 40-41. The amountof heat applied and the time of heat application may vary, and in oneexample is 420 degrees Fahrenheit for two minutes. Alternatively, heatand pressure may be applied as described in the “First and Second Tubeswith Heated Oven” example, or other heat and pressure applications.

After removal from the heated press 196, cooling, and removal from thepress fixture 186, the second layer of elastomeric tube 408 is removedfrom the first layer of elastomeric tube 402, as shown in FIGS. 52 and53. Any of the removal methods as described previously may be used toremove the second layer of elastomeric tube 408 from the first layer ofelastomeric tube 402. A shrink tube 414 may be positioned over orwrapped around the first layer of elastomeric tube 402 and smoothcovered stent 198. The material of the shrink tube 414 may includeshrink silicone, polyimide shrink, shrink polyetheretherketone (PEEK),fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), orpolyethylene terephthalate (PET), and the shrink tube 414 includes adiameter 416. The diameter 416 of the shrink tube 414 is sufficient tobe positioned over the first layer of elastomeric tube 402.

As shown in FIG. 54, a heating source 418, such as a heating gun, isapplied to the shrink tube 414 to shrink the first layer of elastomerictube 402 and apply compression and heat to the smooth covered stent 198.The amount of heat and the time of heat application may vary, and in oneexample, may be 215 degrees Celsius (or 420 degrees Fahrenheit) for fiveminutes when a shrink tube 414 comprising FEP is used. The shrink tube414 is removed from the first layer of elastomeric tube 402, and thenthe first layer of elastomeric tube 402 is removed from the smoothcovered stent 198 using any of the removal methods as describedpreviously. The smooth covered stent 198 is then removed from themandrel 396. As shown in FIGS. 55 and 56, the inner surface 394 of thesmooth covered stent 198 is smooth and the stripes 392 are removed. Inanother example, the strips 392 may be removed from the inner surface394 of the smooth covered stent 198 without use of the press fixture 186and the heated press 196.

FIGS. 57-60 show another example of the slit cannula 300 when only asingle mandrel 420 is used. The first ends 314 of the slits 300 allbegin at the first end 306 of the slit cannula 300. FIG. 58 shows across sectional view of the first end 306 of the slit cannula 300.

The mandrel 420 includes a circular cross-section with a first portion422 and a second portion 424. The first portion 422 includes a diameter426, and the second portion 424 includes a diameter 428. The diameter426 of the first portion 422 is greater than the diameter 428 of thesecond portion 424. The mandrel 420 includes a first end 430, a secondend 432, a tip 434, and a longitudinal length 436, which is defined fromthe first end 430 to the second end 432 of the mandrel 420. Thelongitudinal length 436 of the mandrel 420 is smaller than thelongitudinal length 310 of the slit cannula 300. In an alternativeexample, the mandrel 420 may be permanently fixed with the slit cannulato provide stability.

FIGS. 59 and 60 show the mandrel 420 within the slit cannula 300. Inthis example, the mandrel 420 is positioned within the slit cannula 300after the first layer of elastomeric tube 342, the inner covering 164,and the stent 100 are positioned over the slit cannula 300. The steps aspreviously described can then be used to encapsulate the stent 100,including application of the outer covering 172 and the second layer ofelastomeric tube 380 and the use of the press fixture 186 and the heatedpress 196 to apply pressure and heat.

FIGS. 61-64 show another example of the mandrel 420 including aplurality of splines 438. The number of splines 438 is the same as thenumber of slits 312 of the slit cannula 300. The mandrel 420 with thesplines 438 helps to prevent the plurality of stripes or indentations392 on the inner surface 394 of the smooth covered stent 198 fromforming during compression. FIG. 64 shows a cross-sectional view of themandrel 420 with the splines 438 when positioned within the slit cannula300.

The tables and steps below provide examples of the materials and stepsusing the aforementioned method.

EXAMPLE 3 Self-Expandable Stent, Slit Cannula and Two Mandrels withHandles

Element Specifications Stent 100 inner diameter 102 is 7.6 mm, outerdiameter 104 is 8.0 mm, nominal diameter is 8 mm, longitudinal length126 is 70 mm, self-expanding Slit cannula 300 inner diameter 302 is 3.76mm, outer diameter 304 is 4.76 mm, longitudinal length is 210 mm,material is stainless steel Slits 312 number slits 312 is 10,longitudinal length 318 of slits is 208 mm First mandrel 322longitudinal length 332 is 92 mm, diameter 324 is first portion 323 is6.22 mm, diameter 327 of second portion 325 is 3.175 mm, material isstainless steel, Handle 334 of diameter of slot 340 is 3.20 mm, materialis first mandrel 322 stainless steel First layer of material is siliconewith a durometer of 50 elastomeric tube Shore A, longitudinal length 352is 210 mm, 342 inner diameter 344 is 4.29 mm, outer diameter 346 is 5.31mm Coating MED-6670, thickness is 45 μm Inner covering 164 includesfirst material 166 and second material 168 First material 166 ePTFESecond material 168 FEP Second mandrel 354 longitudinal length 370 is144 mm, diameter 324 is first portion 356 is 6.22 mm, diameter 327 ofsecond portion 358 is 3.175 mm, material is stainless steel, Handle 372of diameter of slot 378 is 3.20 mm, material is second mandrel stainlesssteel 354 Outer covering 172 includes first material 166 and secondmaterial 168 Second layer of material is silicone with a durometer of 20elastomeric tube Shore A, longitudinal length 390 is 114 mm, 380 innerdiameter 382 is 6 mm, outer diameter 384 is 8 mm Tube expander 128 innerdiameter 134 is 14 mm Slot 192 of Press diameter 194 of slot 192 is 9.6mm Fixture 186

Steps:

-   -   The first mandrel 322 is positioned within the slit cannula 300;    -   The coating is applied to the outer diameter 346 of the first        elastomeric tube 342 and then cured;    -   The first layer of elastomeric tube 342 is positioned over the        slit cannula 300;    -   The inner covering 164 is rolled in 70% isopropanol;    -   The inner covering 164 is positioned over and wrapped around a        non-expanded portion of the slit cannula 300 with the first        material 166 of the inner covering 164 in contact with the first        elastomeric tube 342;    -   The stent 100 is positioned over the inner covering 164 and in        contact with the second material 168 of the inner covering 164;    -   The second mandrel 354 is positioned within the slit cannula 300        and radially expands the slit cannula 300, the first layer of        elastomeric tube 342, and the inner covering 164 such that the        inner covering 164 is in contact with the inner diameter 102 of        the stent 100;    -   The outer covering 172 is rolled in 70% isopropanol;    -   The outer covering 172 is positioned over and wrapped around the        stent 100 with the second material 168 in contact with the stent        100 to form the covered stent 174;    -   The coating is applied to the inner diameter 382 of the second        layer of elastomeric tube 380 and then cured;    -   The second layer of elastomeric tube 380 is positioned within        the tube expander 128 including the vacuum 148;    -   The first and second ends 306, 308 of the second layer of        elastomeric tube 380 are rolled up and wrapped around the first        and second ends 138, 140 of the tube expander 128;    -   The vacuum 148 is applied expanding the inner and outer        diameters 382, 384 of second layer of elastomeric tube 380 until        the outer diameter 384 of the second elastomeric tube 380        contacts the inner diameter 134 of the tube expander 128;    -   One of the handles 334, 372 is removed from either the first or        second mandrel 322, 354;    -   The covered stent 174, the first layer of elastomeric tube 342,        the slit cannula 300, and the first and second mandrels 322, 354        are positioned in the tube expander 128;    -   The vacuum 148 is released allowing the inner and outer        diameters 382, 384 of second layer of elastomeric tube 380 to        retract to an unexpanded state and recover to the covered stent        174;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, the slit cannula 300, and the first and        second mandrels 322, 354 are removed from the tube expander 128;    -   One of the handles 344, 372 previously removed is positioned        back on either the first or second mandrel 322, 354;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, the slit cannula 300, and the first and        second mandrels 322, 354 are positioned in a vacuum chamber with        an applied pressure of 600 mmHg (absolute vacuum pressure) for 1        hour;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, the slit cannula 300, and the first and        second mandrels 322, 354 are removed from the vacuum chamber and        positioned in the slot 192 of the press fixture 186 and the        first and second portions 188, 190 of the press fixture 186 are        brought together;    -   The press fixture 186 is positioned in the heated press 196;    -   Pressure is applied to the press fixture 186 to displace the        thickness of second layer of elastomeric tube 380 by 0.005±0.001        inches;    -   Heat is applied to the press fixture 186 to 500±5 degrees        Fahrenheit and is applied for 1 minute time;    -   The press fixture 186 is removed from the heated press 196;    -   The first and second layers of elastomeric tube 342, 380, the        smooth covered stent 198, the slit cannula 300, and the first        and second mandrels 322, 354 are removed from the press fixture        186 and positioned in room temperature water for cooling;    -   One of the handles 334, 372 is removed from either the first or        second mandrel 322, 354;    -   The first and second layers of elastomeric tube 342, 380, the        smooth covered stent 198, the slit cannula 300, and the first        and second mandrels 322, 354 are positioned in the tube expander        128;    -   The vacuum 148 is applied allowing the inner and outer diameters        382, 384 of second layer of elastomeric tube 380 to uniformly        expand;    -   The smooth covered stent 198, the first layer of elastomeric        tube 342, the slit cannula 300, and the first and second        mandrels 322, 354 are removed from the tube expander 128;    -   One of the handles 344, 372 previously removed is positioned        back on either the first or second mandrel 322, 354;    -   The second mandrel 354 is removed from the slit cannula 300; and    -   The smooth covered stent 198 is removed from the slit cannula        300.

EXAMPLE 4 Self-Expandable Stent, Slit Cannula and Single Mandrel withoutHandle

Element Specifications Stent 100 inner diameter 102 is 7.6 mm, outerdiameter 104 is 8.0 mm, nominal diameter is 8 mm, longitudinal length126 is 70 mm, self-expandable Slit cannula 300 inner diameter 302 is3.76 mm, outer diameter 304 is 4.76 mm, longitudinal length is 210 mm,material is stainless steel Slits 312 number slits 312 is 10,longitudinal length 318 of slits is 208 mm Mandrel 420 longitudinallength 436 is 236 mm, diameter 426 of first portion 422 is 6.22 mm,diameter 428 of second portion 424 is 3.175 mm, material is stainlesssteel First layer of material is silicone with a durometer of 50elastomeric tube Shore A, longitudinal length 352 is 210 mm, 342 innerdiameter 344 is 4.29 mm, outer diameter 346 is 5.31 mm Coating MED-6670,thickness is 45 μm Inner covering 164 includes first material 166 andsecond material 168 First material 166 esPTFE Second material 168Polyurethane Outer covering 172 includes first material 166 and secondmaterial 168 Second layer of material is silicone with a durometer of 20elastomeric tube Shore A, longitudinal length 390 is 114 mm, 380 innerdiameter 382 is 6 mm, outer diameter 384 is 8 mm Tube expander 128 innerdiameter 134 is 14 mm Slot 192 of Press diameter 194 of slot 192 is 9.6mm Fixture 186

Steps:

-   -   The coating is applied to the outer diameter 346 of the first        elastomeric tube 342 and then cured;    -   The first layer of elastomeric tube 342 is positioned over the        slit cannula 300;    -   The inner covering 164 is rolled in 70% isopropanol;    -   The inner covering 164 is positioned over and wrapped around the        slit cannula 300 with the first material 166 of the inner        covering 164 in contact with the first elastomeric tube 342;    -   The stent 100 is positioned over the inner covering 164 and in        contact with the second material 168 of the inner covering 164;    -   The mandrel 420 is positioned within the slit cannula 300 and        radially expands the slit cannula 300, the first layer of        elastomeric tube 342, and the inner covering 164 such that the        inner covering 164 is in contact with the inner diameter 102 of        the stent 100;    -   The outer covering 172 is rolled in 70% isopropanol;    -   The outer covering 172 is positioned over and wrapped around the        stent 100 with the second material 168 in contact with the stent        100 to form the covered stent 174;    -   The coating is applied to the inner diameter 382 of the second        layer of elastomeric tube 380 and then cured;    -   The second layer of elastomeric tube 380 is positioned within        the tube expander 128 including the vacuum 148;    -   The first and second ends 306, 308 of the second layer of        elastomeric tube 380 are rolled up and wrapped around the first        and second ends 138, 140 of the tube expander 128;    -   The vacuum 148 is applied expanding the inner and outer        diameters 382, 384 of second layer of elastomeric tube 380 until        the outer diameter 384 of the second elastomeric tube 380        contacts the inner diameter 134 of the tube expander 128;    -   The covered stent 174, the first layer of elastomeric tube 342,        the slit cannula 300, and the mandrel 420 are positioned in the        tube expander 128;    -   The vacuum 148 is released allowing the inner and outer        diameters 382, 384 of second layer of elastomeric tube 380 to        retract to an unexpanded state and recover to the covered stent        174;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, the slit cannula 300, and the mandrel 420 are        removed from the tube expander 128;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, the slit cannula 300, and the first and        second mandrels 322, 354 are positioned in a vacuum chamber with        an applied pressure of 600 mmHg (absolute vacuum pressure) for 1        hour;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, the slit cannula 300, and the mandrel 420 are        removed from the vacuum chamber and positioned in the slot 192        of the press fixture 186 and the first and second portions 188,        190 of the press fixture 186 are brought together;    -   The press fixture 186 is positioned in the heated press 196;    -   Pressure is applied to the press fixture 186 to displace the        thickness of second layer of elastomeric tube 380 by 0.005±0.001        inches;    -   Heat is applied to the press fixture 186 to 390±5 degrees        Fahrenheit and is applied for 1 minute time;    -   The press fixture 186 is removed from the heated press 196;    -   The first and second layers of elastomeric tube 342, 380, the        smooth covered stent 198, the slit cannula 300, and the mandrel        420 are removed from the press fixture 186 and positioned in        room temperature water for cooling;    -   The first and second layers of elastomeric tube 342, 380, the        smooth covered stent 198, the slit cannula 300, and the mandrel        420 are positioned in the tube expander 128;    -   The vacuum 148 is applied allowing the inner and outer diameters        382, 384 of second layer of elastomeric tube 380 to uniformly        expand;    -   The smooth covered stent 198, the first layer of elastomeric        tube 342, the slit cannula 300, and the mandrel 420 are removed        from the tube expander 128;    -   The mandrel 420 is removed from the slit cannula 300; and    -   The smooth covered stent 198 is removed from the slit cannula        300.

Applied Tension to Elastomeric Tube

In an alternative embodiment, when a self-expanding stent is used,tension may be applied to an elastomeric tube positioned on the mandrelrather than use of the slit cannula 300. For example, the first layer ofelastomeric tube 342 is positioned within the tube expander 128including the vacuum 148, and the first and second ends 348, 350 arerolled up and wrapped around the first and second ends 138, 140 of thetube expander 128. The vacuum 148 is applied expanding the inner andouter diameters 344, 346 of the first layer of elastomeric tube 342. Themandrel 150 is positioned in the tube expander 128, and the vacuum 148is released allowing the inner and outer diameters 344, 346 of the firstlayer of elastomeric tube 342 to retract to an unexpanded state andrecover to the mandrel 150. The outer diameter 346 of the first layer ofelastomeric tube 342 on the mandrel 150 is then reduced by applyingtension to the first layer of elastomeric tube 342 to allow the stent100 to slide or otherwise be positioned over the first layer ofelastomeric tube 342. Specifically, the tension applied outer diameter346 of the first layer of elastomeric tube 342 is less than the innerdiameter 102 of the stent 100. The tension may be applied by usingclamps to pull on the first and second ends 348, 350 of the first layerof elastomeric tube 342.

With the tension applied to the first layer of elastomeric tube 342 onthe mandrel 150, the inner covering 164 is positioned over and wrappedaround the first layer of elastomeric tube 342 with the first material166 of the inner covering 164 in contact with the first layer ofelastomeric tube 342, as described previously. The stent 100, which inthis example is a self-expanding stent, is positioned over the innercovering 164 and in contact with the second material 168 of the innercovering 164. After the stent 100 is positioned over the inner covering164, the tension applied to the first layer of elastomeric tube 342 maybe released and the clamps removed. When the tension is released, thefirst layer of elastomeric tube 342 expands to a non-tension appliedstate. After expansion, the inner covering 164 contacts the innerdiameter 102 of the stent 100, and the stent 100 maintains its nominaldiameter and is not significantly expanded. The subsequent stepsdescribed above to form the smooth covered stent 198 may then beapplied, including without limitation the application of the outercovering 172, the application of the second layer of elastomeric tube380, the application of heat and pressure using the press fixture 186and heated press 196, may be used.

First and Second Tubes with Heated Oven

FIGS. 65-74 show another example of a method of making a stent with asmooth cover. FIG. 65 shows the covered stent 174 positioned over themandrel 150 using the process steps as described previously. A firsttube of elastomeric tube 500 is positioned in the tube expander 128. Thefirst tube of elastomeric tube 500 may include the same material as theelastomeric tube 116 previously described. The first tube of elastomerictube 500 includes an inner diameter 502, an outer diameter 504, a firstend 506, a second end 508, and a longitudinal length 510, which isdefined from the first end 506 to the second end 508. The longitudinallength 510 of the first tube 500 is longer than the longitudinal lengthof the covered stent 174 to completely cover the covered stent 174. Inthis example, the stent 100 is a balloon expandable stent. The innerdiameter 502 of the elastomeric tube 500 may range from 2 mm to 15 mm.The outer diameter 504 of the elastomeric tube 500 may range from 3 mmto 21 mm.

A coating, as previously described, that reduces the friction on thesurface of the first tube 500 may be applied to the inner diameter 502of the first tube 500. The coating helps to remove the stickiness ortackiness of the first tube 500, so that the first tube 500 does notstick to the outer covering 172 of the covered stent 174.

As shown in FIG. 67, the first and second ends 506, 508 of the firsttube 500 are wrapped around the first and second ends 138, 140 of thetube expander 128 to seal the first tube 500 to the tube expander 128,and then the vacuum 148 is applied to uniformly expand the inner andouter diameters 502, 504 of the first tube 500. The covered stent 174and the mandrel 150 are then positioned in the tube expander 128 asshown in FIG. 68, and the vacuum source 148 is released to allow thefirst tube 500 to recover to the covered stent 100 as shown in FIG. 69.In its original state, the inner diameter 502 of the first tube 500 issmaller than the diameter 176 of the covered stent 100 and the mandrel150.

A second tube 512 is provided as shown in FIG. 71. The second tube 512may include the same material as the elastomeric tube 116 previouslydescribed, or the second tube 512 may include a shrink tube aspreviously described including shrink silicone, polyimide shrink, shrinkpolyetheretherketone (PEEK), fluorinated ethylene propylene (FEP),polytetrafluoroethylene (PTFE), or polyethylene terephthalate (PET). Thematerial of the second tube 512 has a higher durometer than the materialof the first tube 500. The second tube 512 includes an inner diameter514, an outer diameter 516, a first end 518, a second end 520, and alongitudinal length 522, which is defined from the first end 518 to thesecond end 520. The inner diameter 514 of the second tube 512 may rangefrom 2 mm to 17 mm. The outer diameter 516 of the second tube 512 mayrange from 3 mm to 23 mm.

The longitudinal length 522 is the same as or longer than thelongitudinal length 510 of the first tube 500. The inner diameter 514 ofthe second tube 510 is smaller than the outer diameter 504 of the firsttube 500 such that when the second tube 510 is applied to the first tube500, the second tube 510 compresses the first tube 500 to the coveredstent 174 and compresses the inner and outer coverings 164, 172 of thecovered stent 174 sufficiently together to conform the outer covering174 around the stent 100. When the second tube 512 is a shrink tube, theinner diameter 514 of the shrink tube 512 is initially larger than theouter diameter 504 of the first tube 500 to allow the second tube 512 toposition over the first tube 500. The inner diameter 514 of the shrinktube 512 will decrease when heat is applied to apply compression.

When the second tube 512 includes an elastomeric tube, the second tube512 is positioned in the tube expander to uniformly expand the inner andouter diameters 514, 516 of the second tube 512 as shown in FIGS. 71-73.The mandrel 150 with the covered stent 174 and the first tube 500 isthen positioned in the tube expander 128, and the vacuum source 148 isreleased to allow the inner and outer diameters 514, 516 of the secondtube 512 to return to an unexpanded state and recover to the first tube500. As described previously, when the second tube 512 recovers to thefirst tube 500, the second tube 512 compresses the first tube 500 to thecovered stent 174. FIG. 73 shows the mandrel 150 with the covered stent174 and the first and second tubes 500, 512. When the second tube 512includes a shrink tube, the second tube 512 is positioned over andwrapped around the first tube 500 and the tube expander 128 is not used.If the second tube 512 includes shrink tape rather than a shrink tube,the shrink tape may be wrapped around the first tube 500.

In one example, when the second tube 512 includes an elastomeric tube,prior to applying pressure and heat, the mandrel 150 with the coveredstent 174 and the first and second tubes 500, 512 may be placed in avacuum chamber for a pretreatment vacuum step. The pretreatment vacuumstep may remove any air bubbles from the first and second tubes 500,512. Air bubbles within the first and second tubes 500, 512 may affectheating and bonding of the inner and outer coverings 164, 172 to thestent 100. The vacuum chamber may be any vacuum chamber known in theart, and the mandrel 150 may be positioned on a rack in the vacuumchamber to provide uniform distribution of the pressure around the firstand second tubes 500, 512. In one example, the vacuum pressure appliedmay be approximately 500 to 700 mmHg (vacuum pressure) may be appliedfor approximately 15 minutes to 2 hours. In another example, the vacuumpressure applied may be approximately 600 mmHg (absolute vacuumpressure) for approximately 1 hour. The vacuum pressure applied may varyand may range from approximately 50 mmHg to 760 mmHg (absolute vacuumpressure), and as the vacuum pressure applied increases, the time thevacuum pressure will be applied decreases.

As shown in FIG. 74, to melt the second material 168 of the inner andouter coverings 164, 172 of the covered stent 174, the mandrel 150 withthe covered stent 174 and the first and second tubes 500, 512 arepositioned in an oven 524 on an elevated rack 526 to apply uniform heatto the covered stent 174. The temperature applied may be the same asdescribed previously for approximately 5 minutes. If the second tube 512is a shrink tube, the temperature applied is above the recoverytemperature of the shrink tube. The time will vary based on the meltingtemperature of the second material 168 or above the glass transitiontemperature of the first material 166 if the second material 168 is notused. Thus, the time period of heat application from range from 2 to 30minutes.

After the heat is applied, the mandrel 150 with the smooth covered stent198 and the first and second tubes 500, 512 are removed from the oven524 and cooled. The first and second tubes 500, 512 may then be removedfrom the smooth covered stent 198 using any of the removal methodspreviously described, including use of the tube expander 128. Themandrel 150 is then removed from the smooth covered stent 198.

In another example, the aforementioned method may be used with aself-expanding stent. When a self-expanding stent is used, the slitcannula 300 is used with either the first and second mandrels 322, 354previously described or the single mandrel 420 rather than the mandrel150. In this example, the first and second tubes 500, 512 may beapplied, as described above, to the covered stent 174, the slit cannula300, and the first and second mandrels 322, 354 or the single mandrel420. If the second tube 512 is elastomeric, the first and secondmandrels 322, 354 or the single mandrel 420 and the slit cannula 300with the covered stent 174 and the first and second tubes 500, 512 maybe placed in a vacuum chamber for the pretreatment vacuum step. Afterremoval from the vacuum chamber, heat may be applied as described aboveusing the oven 524 and the first and second tubes 500, 512 may beremoved from the smooth covered stent 198 using any of the removalmethods previously described, including use of the tube expander 128.After the removal of the first and second tubes 500, 512, if the firstand second mandrels 322, 354 are used, rather than the single mandrel420, the smoother covered stent 198 may include the plurality of stripesor indentations 392 on the inner surface 394 of the smooth covered stent198 from compression against the slits 312 of the slit cannula 300. Theplurality of stripes or indentations 392 may be removed using the stepspreviously described above.

In an alternative example, as described previously above, if aself-expanding stent is used, tension may be applied to an additionalelastomeric tube, or a third tube, positioned on the mandrel rather thanuse of the slit cannula 300. Specifically, the third tube may bepositioned around the mandrel 150 via the tube expander 128 includingthe vacuum 148, as described previously above, prior to placement of theinner covering 164 over the mandrel 150. After placement of the thirdtube around the mandrel 150, tension is applied to the third tube toradially decrease the outer diameter of the third tube to allow thestent 100 to slide or otherwise be positioned over the third tube on themandrel 150. Specifically, the tension applied outer diameter of thethird tube is less than the inner diameter 102 of the stent 100. Thetension may be applied by using clamps to pull on the ends of the secondelastomeric tube.

With the tension applied to the third tube on the mandrel 150, the innercovering 164 is positioned over and wrapped around the third tube withthe first material 166 of the inner covering 164 in contact with thethird tube, as described previously. The stent 100 is positioned overthe inner covering 164 and in contact with the second material 168 ofthe inner covering 164. After the stent 100 is positioned over the innercovering 164, the tension applied to the third tube may be released andthe clamps removed. When the tension is released, the third tuberadially expands to a non-tension applied state. After expansion, theinner covering 164 contacts the inner diameter 102 of the stent 100, andthe stent 100 maintains its nominal diameter and is not significantlyexpanded. The subsequent steps described above to form the smoothcovered stent 198 may then be applied, including without limitation theapplication of an outer covering 172, the application of the first andsecond tubes 500, 512, and the application of heat using the oven 524,may be used.

The tables and steps below provide examples of the materials and stepsusing the aforementioned method.

EXAMPLE 5 Balloon-Expandable Stent, First and Second Tubes, and Innerand Outer Coverings with First and Second Materials

Element Specifications Stent 100 inner diameter 102 is 8.0 mm, outerdiameter 104 is 8.4 mm, nominal diameter is 8 mm, longitudinal length126 is 30 mm, balloon-expandable Mandrel 150 diameter is 8 mm, thematerial is stainless steel First tube 500 material is silicone with adurometer of 20 Shore A, longitudinal length 510 is 75 mm, innerdiameter 502 is 6 mm, outer diameter 504 is 8 mm Coating MED-6670,thickness is 45 μm Inner covering 164 includes first material 166 andsecond material 168 First material 166 esPTFE Second material 168Polyurethane Outer covering 172 includes first material 166 and secondmaterial 168 Second tube 512 material is silicone with a durometer of 25Shore A, longitudinal length 522 is 75 mm, inner diameter 514 is 6 mm,outer diameter 516 is 8 mm Tube expander 128 inner diameter 134 is 14 mm

Steps:

-   -   The inner covering 164 is rolled in 70% isopropanol;    -   The inner covering 164 is positioned over and wrapped around the        mandrel 150 with the first material 166 of the inner covering        164 in contact with the mandrel 150;    -   The stent 100 is initially slightly over-expanded and then        positioned over the inner covering 164 and in contact with the        second material 168 of the inner covering 164;    -   An Iris crimper is used to secure the stent 100 to the inner        covering 164;    -   The outer covering 172 is rolled in 70% isopropanol;    -   The outer covering 172 is positioned over and wrapped around the        stent 100 with the second material 168 in contact with the stent        100 to form the covered stent 174;    -   The coating is applied to the inner diameter 502 of the first        tube 500 and then cured;    -   The first tube 500 is positioned within the tube expander 128        including the vacuum 148;    -   The first and second ends 506, 508 of the first tube 500 are        rolled up and wrapped around the first and second ends 138, 140        of the tube expander 128;    -   The vacuum 148 is applied expanding the inner and outer        diameters 502, 504 of the first tube 500 until the outer        diameter 504 of the first tube 500 contacts the inner diameter        134 of the tube expander 128;    -   The covered stent 174 and the mandrel 150 are positioned in the        tube expander 128;    -   The vacuum 148 is released allowing the inner and outer        diameters 502, 504 of the first tube 500 to retract to an        unexpanded state and recover to the covered stent 174;    -   The first tube 500, the covered stent 174, and the mandrel 150        are removed from the tube expander 128;    -   The coating is applied to the inner diameter 514 of the second        tube 512 and then cured;    -   The second tube 512is positioned within the tube expander 128        including the vacuum 148;    -   The first and second ends 518, 520 of the second tube 512 are        rolled up and wrapped around the first and second ends 138, 140        of the tube expander 128;    -   The vacuum 148 is applied expanding the inner and outer        diameters 514, 516 of the second tube 512 until the outer        diameter 516 of the second tube 512 contacts the inner diameter        134 of the tube expander 128;    -   The first tube 500, the covered stent 174, and the mandrel 150        are positioned in the tube expander 128;    -   The vacuum 148 is released allowing inner and outer diameters        514, 516 of the second tube 512 to retract to an unexpanded        state and recover to the first tube 500 and the covered stent        174;    -   The first and second tubes 500, 512 the covered stent 174, and        the mandrel 150 are removed from the tube expander 128;    -   The first and second tubes 500, 512, the covered stent 174, and        the mandrel 150 are positioned in a vacuum chamber with an        applied pressure of 600 mmHg (absolute vacuum pressure) for 1        hour;    -   The first and second tubes 500, 512, the covered stent 174, and        the mandrel 150 are removed from the vacuum chamber and        positioned on the rack 526 in the heated oven 524 and heated to        390±5 degrees Fahrenheit and is applied for 5 minutes time;    -   The first and second tubes 500, 512, the smooth covered stent        198, and the mandrel 150 are removed from the heated oven 524        and then compressed air or freeze spray is applied for cooling;    -   The first and second tubes 500, 512, the smooth covered stent        198, and the mandrel 150 are positioned in the tube expander        128;    -   The vacuum 148 is applied allowing the inner and outer diameters        514, 516 of the second tube 512 to expand away from the first        tube 500;    -   The first tube 500, the smooth covered stent 198, and the        mandrel 150 are removed from the tube expander 128;    -   The vacuum 148 is released allowing the inner and outer        diameters 514, 516 of the second tube 512 to retract to an        unexpanded state and the second tube 512 is removed from the        tube expander 128;    -   The first tube 500, the smooth covered stent 198, and the        mandrel 150 are positioned in the tube expander 128;    -   The vacuum 148 is applied allowing the inner and outer diameters        502, 504 of the first tube 500 to expand away from the smooth        covered stent 198;    -   The smooth covered stent 198 and the mandrel 150 are removed        from the tube expander 128; and    -   The mandrel 150 is removed from the smooth covered stent 198.

EXAMPLE 6 Balloon-Expandable Stent, First and Second Tubes, and Innerand Outer Coverings with First Material

Element Specifications Stent 100 inner diameter 102 is 8.0 mm, outerdiameter 104 is 8.4 mm, nominal diameter is 8 mm, longitudinal length126 is 30 mm, balloon-expandable Mandrel 150 diameter is 8 mm, thematerial is stainless steel First tube 500 material is silicone with adurometer of 20 Shore A, longitudinal length 510 is 75, inner diameter502 is 6 mm, outer diameter 504 is 8 mm Coating MED-6670, thickness is45 μm Inner covering 164 includes first material 166 First material 166PET Outer covering 172 includes first material 166 Second tube 512material is silicone with a durometer of 25 Shore A, longitudinal length522 is 75 mm, inner diameter 514 is 6 mm, outer diameter 516 is 8 mmTube expander 128 inner diameter 134 is 14 mm

Steps:

-   -   The inner covering 164 is rolled in 70% isopropanol;    -   The inner covering 164 is positioned over and wrapped around the        mandrel 150;    -   The stent 100 is initially slightly over-expanded and then        positioned over the inner covering 164;    -   An Iris crimper is used to secure the stent 100 to the inner        covering 164;    -   The outer covering 172 is rolled in 70% isopropanol;    -   The outer covering 172 is positioned over and wrapped around the        stent 100 to form the covered stent 174;    -   The coating is applied to the inner diameter 502 of the first        tube 500 and then cured;    -   The first tube 500 is positioned within the tube expander 128        including the vacuum 148;    -   The first and second ends 506, 508 of the first tube 500 are        rolled up and wrapped around the first and second ends 138, 140        of the tube expander 128;    -   The vacuum 148 is applied expanding the inner and outer        diameters 502, 504 of the first tube 500 until the outer        diameter 504 of the first tube 500 contacts the inner diameter        134 of the tube expander 128;    -   The covered stent 174 and the mandrel 150 are positioned in the        tube expander 128;    -   The vacuum 148 is released allowing the inner and outer        diameters 502, 504 of the first tube 500 to retract to an        unexpanded state and recover to the covered stent 174;    -   The first tube 500, the covered stent 174, and the mandrel 150        are removed from the tube expander 128;    -   The coating is applied to the inner diameter 514 of the second        tube 512 and then cured;    -   The second tube 512 is positioned within the tube expander 128        including the vacuum 148;    -   The first and second ends 518, 520 of the second tube 512 are        rolled up and wrapped around the first and second ends 138, 140        of the tube expander 128;    -   The vacuum 148 is applied uniformly expanding the inner and        outer diameters 514, 516 of the second tube 512 until the outer        diameter 516 of the second tube 512 contacts the inner diameter        134 of the tube expander 128;    -   The first tube 500, the covered stent 174, and the mandrel 150        are positioned in the tube expander 128;    -   The vacuum 148 is released allowing inner and outer diameters        514, 516 of the second tube 512 to retract to an unexpanded        state and recover to the first tube 500 and the covered stent        174;    -   The first and second tubes 500, 512 the covered stent 174, and        the mandrel 150 are removed from the tube expander 128;    -   The first and second tubes 500, 512, the covered stent 174, and        the mandrel 150 are positioned in a vacuum chamber with an        applied pressure of 600 mmHg (absolute vacuum pressure) for 1        hour;    -   The first and second tubes 500, 512, the covered stent 174, and        the mandrel 150 are removed from the vacuum chamber and        positioned on the rack 526 in the heated oven 524 and heated to        365±5 degrees Fahrenheit and is applied for 5 minutes time;    -   The first and second tubes 500, 512, the smooth covered stent        198, and the mandrel 150 are removed from the heated oven 524        and then compressed air or freeze spray is applied for cooling;    -   The first and second tubes 500, 512, the smooth covered stent        198, and the mandrel 150 are positioned in the tube expander        128;    -   The vacuum 148 is applied allowing the inner and outer diameters        514, 516 of the second tube 512 to expand away from the first        tube 500;    -   The first tube 500, the smooth covered stent 198, and the        mandrel 150 are removed from the tube expander 128;    -   The vacuum 148 is released allowing the inner and outer        diameters 514, 516 of the second tube 512 to retract to an        unexpanded state and the second tube 512 is removed from the        tube expander 128;    -   The first tube 500, the smooth covered stent 198, and the        mandrel 150 are positioned in the tube expander 128;    -   The vacuum 148 is applied allowing the inner and outer diameters        502, 504 of the first tube 500 to expand away from the smooth        covered stent 198;    -   The smooth covered stent 198 and the mandrel 150 are removed        from the tube expander 128; and    -   The mandrel 150 is removed from the smooth covered stent 198.

Internal Pressure Application

FIGS. 77-94 show another example of a method of making a stent with asmooth cover. FIG. 77 shows a tapered rod 600, a first hollow mandrel602, a second hollow mandrel 604, and the stent 100, describedpreviously above. In this example, the stent 100 is a self-expandingstent. As described in more detail below, the use of the tapered rod600, the first hollow mandrel 602, and the second hollow mandrel 604allow for gradual radial expansion of the inner and outer diameters 102,104 of the stent 100. The tapered rod 600 includes a first end 606, asecond end 608, a length 610 extending from the first end 606 to thesecond end 608, and a diameter 612. The diameter 612 of the tapered rod610 is less than the inner and outer diameters 102, 104 of the stent100. A handle 614 is positioned over or otherwise connected to the firstend 606 of the tapered rod 600. The second end 608 of the tapered rod isa tapered end 616. The material of the tapered rod 600 and the handle614 may include glass, metal, stainless steel, brass and/or an alloy.

The first hollow mandrel 602 includes a first end 617, a second end 618,a length 620 extending from the first end 617 to the second end 618, aninner diameter 622, and an outer diameter 624. The first end 617 of thefirst hollow mandrel 602 may include a tapered portion 619, as shown inFIG. 77. The inner diameter 622 of the first hollow mandrel 602 isgreater than the diameter 612 of the tapered rod 600 such that thetapered rod 600 may be inserted into the first hollow mandrel 602.

The second hollow mandrel 604 includes a first end 626, a second end628, a length 630 extending from the first end 626 to the second end628, an inner diameter 632, and an outer diameter 634. The second end628 of the second hollow mandrel 604 may include a tapered portion 629,as shown in FIG. 77. The inner diameter 632 of the second hollow mandrel604 is greater than the outer diameter 624 of the first hollow mandrel602 such that the first hollow mandrel 602 may be inserted into thesecond hollow mandrel 604. The material of the first hollow mandrel 602and the second hollow mandrel 604 may include glass, metal, stainlesssteel, brass and/or an alloy. In an alternative embodiment, a hollowmandrel with a gradually expanding outer diameter along its length maybe used rather than the first hollow mandrel 602 and the second hollowmandrel 604 to allow for gradual radial expansion of the stent 100.

FIG. 78 shows the stent 100 to be positioned over the tapered end 616and onto the tapered rod 600. As described previously, the diameter 612of the tapered rod 600 is less than the inner and outer diameters 102,104 of the stent 100 such that the stent 100 may slide onto the taperedrod 600 without the inner and outer diameters 102, 104 of the stent 100significantly expanding. The tapered rod 600 with the stent 100 may beinserted into the first end 617 having the tapered portion 619 of thefirst hollow mandrel 602, as shown in FIG. 79. FIG. 80 shows thattapered end 616 of the tapered rod 600 positioned within the firsthollow mandrel 602. As described previously, the diameter 612 of thetapered rod 600 is less than the inner diameter 622 of the first hollowmandrel 602 such that the tapered rod 600 may be inserted into the firsthollow mandrel 602. The stent 100 may then slide along the tapered rod600 and onto the first hollow mandrel 602, as shown in FIG. 81, whichallows for gradual radial expansion of the stent 100. After the stent100 is positioned over the first hollow mandrel 602, the tapered rod 600is removed from the first hollow mandrel 602.

The first hollow mandrel 602 with the stent 100 may be inserted into thesecond end 628 having the tapered portion 629 of the second hollowmandrel 604, as shown in FIG. 82. As described previously, the outerdiameter 624 of the first hollow mandrel 602 is less than the innerdiameter 632 of the second hollow mandrel 604 such that the first hollowmandrel 602 may be inserted into the second hollow mandrel 604. Thestent 100 may then slide along the first hollow mandrel 602 and onto thesecond hollow mandrel 604, as shown in FIG. 83, which allows for gradualradial expansion of the stent 100. After the stent 100 is positionedover the second hollow mandrel 604, the first hollow mandrel 602 may beremoved from the second hollow mandrel 604, as shown in FIG. 84.

As shown in FIG. 85, the mandrel 150 with the first layer of elastomerictube 342 positioned over the mandrel 150 and the inner covering 164wrapped around the first layer of elastomeric tube 342 is provided. Asdescribed previously, the first layer of elastomeric tube 342 mayinclude the same material as the elastomeric tube 116, and the coatingmay be applied to the outer diameter 346 of the first layer ofelastomeric tube 342 to remove the stickiness or tackiness of the firstlayer of elastomeric tube 342 so that the first layer of elastomerictube 342 does not stick to the inner covering 164. The first layer ofelastomeric tube 342 may be positioned over the mandrel 150 using stepsdescribed previously.

Also, as previously described, the inner covering 164, including thefirst material 166 and the second material 168, is positioned over andwrapped around the first layer of elastomeric tube 342 such that thefirst material 166 is in contact with the first layer of the elastomerictube 342. Additional layers may also be added such that the first andsecond materials 166, 168 of the layers maintain an alternating patternover the stent 100, as described previously. To keep the layers inplace, the soldering iron, described previously, may be used to tack orotherwise adhere edges of the inner covering 164. In an alternativeembodiment, the mandrel 150 is not used and the inner covering 164 iswrapped around the first layer of elastomeric tube 342 without themandrel 150 beneath the first layer of elastomeric tube.

The mandrel 150 with the first layer of elastomeric tube 342 and theinner covering 164 is positioned within the second hollow mandrel 604,as shown in FIG. 86. Once the second hollow mandrel 604 is positionedover the inner covering 164, the second hollow mandrel 604 is pulledaway such that the stent 100 is positioned over the inner covering 164,as shown in FIG. 87, and the stent 100 recovers to its nominal diameter.When the stent 100 is positioned over the inner covering 164, the secondmaterial 168 of the inner covering 164 is in contact with the stent 100.The mandrel 150 may then be removed from the first layer of elastomerictube 342 by pulling the mandrel 150 from beneath the first layer ofelastomeric tube 342, as shown in FIG. 88.

In one example, freeze spray or liquid nitrogen may be applied to thestent 100 positioned on the second hollow mandrel 604 prior to removingthe second hollow mandrel 604 from beneath the stent 100. The freezespray or liquid nitrogen freezes the stent 100 in its expanded state,which facilitates positioning and placement of the stent 100 over theinner covering 164. When the stent 100 returns to room temperature, thestent 100 recovers to its nominal diameter and to the inner covering164.

A support mandrel 636 is inserted into the first layer of elastomerictube 342, as shown in FIG. 89. The support mandrel 636 includes a firstend 638, a second end 640, a length 642 extending from the first end 638to the second end 640, and an outer diameter 644 is shown in FIG. 89.The outer diameter 644 of the support mandrel 636 is less than the innerdiameter 344 of the first layer of elastomeric tube 342 in an unexpandedstate such that the support mandrel 636 may slide into the first layerof elastomeric tube 342. In this example, the support mandrel 636 ishollow and includes an inner diameter and a plurality of holes 646 alongits length 642, as shown in FIG. 89. The plurality of holes 646 withinthe hollow support mandrel 636 allow for air, gas or hydraulic pressureto contact the first layer of elastomeric tube 342 and allow forexpansion of the first layer of elastomeric tube 342. The supportmandrel 636 provides support to the stent 100 during the pressurizationand heating process. In alternative examples, the support mandrel may besolid and/or include supporting rib elements that extend along itslength.

In another alternative example, the support mandrel 636 may be usedrather than the mandrel 150 such that the first layer of elastomerictube 342 is positioned over the support mandrel 636, the inner covering164 is wrapped around the first layer of elastomeric tube 342, and thestent 100 is positioned over the inner covering 164, as describedpreviously above. In this alternative example, the support mandrel 636would not be removed prior to applying heat and pressure and wouldremain within the first layer of elastomeric tube 342 until after heatand pressure are applied, as described in more detail below.

The outer covering 172, including the first material 166 and the secondmaterial 168, is positioned over and wrapped around the stent 100 asdescribed previously and as shown in FIG. 89 to form the covered stent174. The second material 168 is in contact with the stent 100, and thefirst material 166 of the outer covering 172 is not in contact with thestent 100. As described previously, additional layers may also be addedsuch that the first and second materials 166, 168 of the layers maintainan alternating pattern over the stent 100. To keep the layers in place,the soldering iron, described previously, may be used to tack orotherwise adhere edges of the outer covering 172.

The second layer of elastomeric tube 380, as described previously, ispositioned over the covered stent 174 and the first layer of elastomerictube 342 as shown in FIGS. 89-90. The inner diameter 382 of the secondlayer of elastomeric tube 380 is greater than the outer diameter 104 ofthe stent 100 with the outer covering 172 applied such that the secondlayer of elastomeric tube 380 may be positioned over the outer covering172 and the stent 100. In an alternative embodiment, if the innerdiameter 382 of the second layer of elastomeric tube 380 is smaller thanor the same as the outer diameter 104 of the stent with the outercovering 172 applied, then the tube expander 128 may be used to radiallyexpand the second layer of elastomeric tube 380 to be positioned overthe outer covering 172 and the stent 100, as described previously. Inone example, prior to applying pressure and heat, the pretreatmentvacuum step may be used, including the vacuum chamber, to remove any airbubbles from the first and second layers of elastomeric tube 324, 380,as described previously.

As described previously, the second layer of elastomeric tube 380 mayinclude the same material as the elastomeric tube 116, and the coatingmay be applied to the inner diameter 382 of the second layer ofelastomeric tube 380 to remove the stickiness or tackiness of the secondlayer of elastomeric tube 380 so that the second layer of elastomerictube 380 does not stick to the outer covering 172. In one example, thefirst layer of elastomeric tube 342 includes a durometer smaller thanthe durometer of the second layer of elastomeric tube 380. Specifically,the durometer of the first layer of elastomeric tube 342 may be 25 ShoreA, and the durometer of the second layer of elastomeric tube 380 may be30 Shore A. In an alternative example, the durometer of the first layerof elastomeric tube 342 is greater than the durometer of the secondlayer of elastomeric tube 380. Specifically, the durometer of the firstlayer of elastomeric tube 342 may be 50 Shore A, and the durometer ofthe second layer of elastomeric tube 380 may be 25 Shore A.

To apply pressure and heat to the first and second layers of elastomerictube 324, 380 and the covered stent 174, a pair of barb fittings 648 areinserted into the first ends 348, 386 and the second ends 350, 388 ofthe first and second layers of elastomeric tube 324, 380, as shown inFIG. 91. The barb fittings 648 are barb fittings known in the artincluding hose barb fittings. A cap 650 is attached to the barb fitting648 that is inserted into the first ends 348, 386 of the first andsecond layers of elastomeric tube 324, 380. The cap 650 acts as a plugto seal off the first ends 348, 386 of the second and second layers ofelastomeric tube 324, 380. A tubing line 652 is attached to the barbfittings 648 that is inserted into the second ends 350, 388 of the firstand second layers of elastomeric tube 324, 380, as shown in FIG. 91. Thetubing line 652 allows pressure, such as air, gas or hydraulic pressure,to enter into the first layer of elastomeric tube 324. A safety guard(not shown) may be positioned on the barb fittings 648 to secure theposition of the barb fittings 648 to the first and second layers ofelastomeric tube 324, 380.

The first and second layers of elastomeric tube 324, 380, the coveredstent 174, the support mandrel 636, and the barb fittings 648 may beinserted into the slot 192 of the press fixture 186, as shown in FIG.92. In this example, the outer diameter of the first and second layersof elastomeric tube 324, 380 and the covered stent 174 is less than thediameter 194 of the slot 192 such that there is space for the outerdiameter of the first and second layers of elastomeric tube 324, 380 andthe covered stent 174 to radially expand within the slot 192 whenpressure is applied. After the press fixture 186 is closed, as shown inFIG. 93, the press fixture 186 may be positioned in the heated press196, as described previously. Heat may be applied via the heated press196, and pressure is applied via the tubing line 652 to apply pressureinternally to the first layer of elastomeric tube 324. The internalpressure causes the first layer of elastomeric tube 324 to expandagainst the inner covering 164 toward the second layer of elastomerictube 380. As described previously, the heat and pressure uniformlyencapsulate and compress the inner and outer coverings 164, 172 and thestent 100 together to form the smooth covered stent 198, as shown inFIG. 94.

After removal from the heated press 196, cooling, and removal from thepress fixture 186, the barb fittings 648, including the cap 650 andtubing line 652, are also removed from the first and second layers ofelastomeric tube 324, 380 and the support mandrel 636 is also removed.The first and second layers of elastomeric tube 324, 380 are removedfrom the smooth covered stent 198 using any of the removal methods asdescribed previously.

In an alternative example, when a self-expanding stent is used, tensionmay be applied to an elastomeric tube positioned on the mandrel ratherthan use of the tapered rod 600, the first hollow mandrel 602 and thesecond hollow mandrel 604. For example, the first layer of elastomerictube 342 is positioned over the mandrel 150 via the tube expander 128including the vacuum 148. The outer diameter 346 of the first layer ofelastomeric tube 342 on the mandrel 150 is then reduced by applyingtension to the first layer of elastomeric tube 342 to allow the stent100 to slide or otherwise be positioned over the first layer ofelastomeric tube 342. Specifically, the tension applied outer diameter346 of the first layer of elastomeric tube 342 is less than the innerdiameter 102 of the stent 100. The tension may be applied by usingclamps to pull on the first and second ends 348, 350 of the first layerof elastomeric tube 342.

With the tension applied to the first layer of elastomeric tube 342 onthe mandrel 150, the inner covering 164 is positioned over and wrappedaround the first layer of elastomeric tube 342 with the first material166 of the inner covering 164 in contact with the first layer ofelastomeric tube 342, as described previously. The stent 100, which inthis example is a self-expanding stent, is positioned over the innercovering 164 and in contact with the second material 168 of the innercovering 164. After the stent 100 is positioned over the inner covering164, the tension applied to the first layer of elastomeric tube 342 maybe released and the clamps removed. When the tension is released, thefirst layer of elastomeric tube 342 expands to a non-tension appliedstate. After expansion, the inner covering 164 contacts the innerdiameter 102 of the stent 100, and the stent 100 maintains its nominaldiameter and is not significantly expanded. The subsequent stepsdescribed above to form the smooth covered stent 198 may then beapplied, including without limitation the removal of the mandrel 150,the positioning of the support mandrel 636 within the first layer ofelastomeric tube 342, the positioning of the second layer of elastomerictube 380, and the application of heat and internal pressure using thebarb fittings 648, the cap 650, the tubing line 652, the press fixture186, and the heated press 196, may be used.

The tables and steps below provide examples of the materials and stepsusing the aforementioned method.

EXAMPLE 7 Self-Expanding Stent, First and Second Tubes, Inner and OuterCoverings with First and Second Materials, and Internal Pressurization

Element Specifications Stent 100 inner diameter 102 is 7.6 mm, outerdiameter 104 is 8 mm, nominal diameter is 8 mm, longitudinal length 126is 30 mm, self-expanding Tapered Rod 600 diameter 612 is 8.2 mm,material is stainless steel First Hollow outer diameter 624 is 9.5 mm,inner diameter 622 Mandrel 602 is 7.8 mm, material is brass SecondHollow outer diameter 634 is 10.3 mm, inner diameter Mandrel 604 632 is9.5 mm, material is brass First layer of material is silicone with adurometer of 25 elastomeric tube Shore A, longitudinal length 352 is5.25 inches, 342 inner diameter 344 is 6 mm, outer diameter 346 is 8 mmCoating MED-6670, thickness is 45 μm Inner covering 164 includes firstmaterial 166 and second material 168 First material 166 esPTFE Secondmaterial 168 Polyurethane Outer covering 172 includes first material 166and second material 168 Second layer of material is silicone with adurometer of 30 elastomeric tube Shore A, longitudinal length 390 is 5.5inches, 380 inner diameter 382 is 6 mm, outer diameter 384 is 8 mmSupport mandrel 636 length 642 is less than 30 mm, diameter 644 is 4.17mm Slot 192 of Press diameter 194 of slot 192 is 9.64 mm Fixture 186

Steps:

-   -   The coating is applied to the outer diameter 346 of the first        elastomeric tube 342 and then cured;    -   The first layer of elastomeric tube 342 is positioned over the        mandrel 150;    -   The inner covering 164 is rolled in 100% isopropanol;    -   The inner covering 164 is positioned over and wrapped around the        first elastomeric tube 342 with the first material 166 of the        inner covering 164 in contact with the first elastomeric tube        342;    -   The stent 100 is positioned on the tapered rod 600;    -   The tapered end 616 of the tapered rod 600 is inserted into the        first end 617 of the first hollow mandrel 602;    -   The stent 100 is pushed along the tapered rod 600 onto the first        hollow mandrel 602;    -   The tapered rod 600 is removed from the first hollow mandrel        602;    -   The first end 617 of the first hollow mandrel 602 is inserted        into the second end 628 of the second hollow mandrel 604;    -   The stent 100 is pushed along the first hollow mandrel 602 onto        the second hollow mandrel 604;    -   The first hollow mandrel 602 is removed from the second hollow        mandrel 604;    -   The mandrel 150 with the first layer of elastomeric tube 342 and        the inner covering 164 is inserted into the second end 628 of        the second hollow mandrel 604 until the second hollow mandrel        604 is substantially covering the inner covering 164;    -   The stent 100 is held in place while the second hollow mandrel        604 is removed from beneath the stent 100 such that the stent        100 recovers to and is positioned over the inner covering 164        and in contact with the second material 168 of the inner        covering 164;    -   The mandrel 150 is removed from the first layer of elastomeric        tube 342;    -   The support mandrel 636 is inserted into the first layer of        elastomeric tube 342;    -   The outer covering 172 is rolled in 100% isopropanol;    -   The outer covering 172 is positioned over and wrapped around the        stent 100 with the second material 168 in contact with the stent        100 to form the covered stent 174;    -   The coating is applied to the inner diameter 382 of the second        layer of elastomeric tube 380 and then cured;    -   The second layer of elastomeric tube 380 is positioned over the        outer covering 172;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, and the support mandrel 636 are positioned in        a vacuum chamber with an applied pressure of 600 mmHg (absolute        vacuum pressure) for one (1) hour;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, and the support mandrel 636 are removed from        the vacuum chamber;    -   The barb fittings 648 are inserted into the first ends 348, 386        and the second ends 350, 388 of the first and second layers of        elastomeric tube 342, 380;    -   The cap 650 is connected to one of the barb fittings 648 and the        tubing line 652 is connected to the other of the barb fittings        648;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, the support mandrel 636, the barb fittings        648, the cap 650, and the tubing line 652 are positioned in the        slot 192 of the press fixture 186 and the first and second        portions 188, 190 of the press fixture 186 are brought together;    -   The press fixture 186 is positioned in the heated press 196;    -   Air pressure of approximately 35 PSI is applied to the tubing        line 642 for approximately 1 minute;    -   Heat is applied to the press fixture 186 to 390±5 degrees        Fahrenheit and is applied for 1 minute time;    -   The press fixture 186 is removed from the heated press 196;    -   The barb fittings 648 are removed from the first ends 348, 386        and the second ends 350, 388 of the first and second layers of        elastomeric tube 342, 380;    -   The support mandrel 636 is removed from the first layer of        elastomeric tube 342;    -   The first and second layers of elastomeric tube 342, 380 and the        covered stent 174 are removed from the press fixture 186 and        positioned in room temperature water for cooling; and    -   The first and second layers of elastomeric tube 342, 380 are        removed from the smooth covered stent 198.

EXAMPLE 8 Self-Expanding Stent, First and Second Tubes, Inner and OuterCoverings with First and Second Materials, and Internal Pressurization

Element Specifications Stent 100 inner diameter 102 is 7.6 mm, outerdiameter 104 is 8 mm, nominal diameter is 8 mm, longitudinal length 126is 30 mm, self-expanding Tapered Rod 600 diameter 612 is 8.2 mm,material is stainless steel First Hollow outer diameter 624 is 9.5 mm,inner diameter 622 Mandrel 602 is 7.8 mm, material is brass SecondHollow outer diameter 634 is 10.3 mm, inner diameter Mandrel 604 632 is9.5 mm, material is brass First layer of material is silicone with adurometer of 50 elastomeric tube Shore A, longitudinal length 352 is5.25 inches, 342 inner diameter 344 is 4.76 mm, outer diameter 346 is7.94 mm Coating MED-6670, thickness is 45 μm Inner covering 164 includesfirst material 166 and second material 168 First material 166 esPTFESecond material 168 Polyurethane Outer covering 172 includes firstmaterial 166 and second material 168 Second layer of material issilicone with a durometer of 25 elastomeric tube Shore A, longitudinallength 390 is 5.5 inches, 380 inner diameter 382 is 6 mm, outer diameter384 is 8 mm Support mandrel 636 length 642 is less than 30 mm, diameter644 is 4.17 mm Slot 192 of Press diameter 194 of slot 192 is 9.64 mmFixture 186

Steps:

-   -   The coating is applied to the outer diameter 346 of the first        elastomeric tube 342 and then cured;    -   The first layer of elastomeric tube 342 is positioned over the        mandrel 150;    -   The inner covering 164 is rolled in 70% isopropanol;    -   The inner covering 164 is positioned over and wrapped around the        first elastomeric tube 342 with the first material 166 of the        inner covering 164 in contact with the first elastomeric tube        342;    -   The stent 100 is positioned on the tapered rod 600;    -   The tapered end 616 of the tapered rod 600 is inserted into the        first end 617 of the first hollow mandrel 602;    -   The stent 100 is pushed along the tapered rod 600 onto the first        hollow mandrel 602;    -   The tapered rod 600 is removed from the first hollow mandrel        602;    -   The first end 617 of the first hollow mandrel 602 is inserted        into the second end 628 of the second hollow mandrel 604;    -   The stent 100 is pushed along the first hollow mandrel 602 onto        the second hollow mandrel 604;    -   The first hollow mandrel 602 is removed from the second hollow        mandrel 604;    -   The mandrel 150 with the first layer of elastomeric tube 342 and        the inner covering 164 is inserted into the second end 628 of        the second hollow mandrel 604 until the second hollow mandrel        604 is substantially covering the inner covering 164;    -   The stent 100 is held in place while the second hollow mandrel        604 is removed from beneath the stent 100 such that the stent        100 recovers to and is positioned over the inner covering 164        and in contact with the second material 168 of the inner        covering 164;    -   The mandrel 150 is removed from the first layer of elastomeric        tube 342;    -   The support mandrel 636 is inserted into the first layer of        elastomeric tube 342;    -   The outer covering 172 is rolled in 70% isopropanol;    -   The outer covering 172 is positioned over and wrapped around the        stent 100 with the second material 168 in contact with the stent        100 to form the covered stent 174;    -   The coating is applied to the inner diameter 382 of the second        layer of elastomeric tube 380 and then cured;    -   The second layer of elastomeric tube 380 is positioned over the        outer covering 172;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, and the support mandrel 636 are positioned in        a vacuum chamber with an applied pressure of 600 mmHg (absolute        vacuum pressure) for one (1) hour;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, and the support mandrel 636 are removed from        the vacuum chamber;    -   The barb fittings 648 are inserted into the first ends 348, 386        and the second ends 350, 388 of the first and second layers of        elastomeric tube 342, 380;    -   The cap 650 is connected to one of the barb fittings 648 and the        tubing line 652 is connected to the other of the barb fittings        648;    -   The first and second layers of elastomeric tube 342, 380, the        covered stent 174, the support mandrel 636, the barb fittings        648, the cap 650, and the tubing line 652 are positioned in the        slot 192 of the press fixture 186 and the first and second        portions 188, 190 of the press fixture 186 are brought together;    -   The press fixture 186 is positioned in the heated press 196;    -   Air pressure of approximately 35 PSI is applied to the tubing        line 642 for approximately 5 minutes;    -   Heat is applied to the press fixture 186 to 390±5 degrees        Fahrenheit and is applied for 5 minutes;    -   The press fixture 186 is removed from the heated press 196;    -   The barb fittings 648 are removed from the first ends 348, 386        and the second ends 350, 388 of the first and second layers of        elastomeric tube 342, 380;    -   The support mandrel 636 is removed from the first layer of        elastomeric tube 342;    -   The first and second layers of elastomeric tube 342, 380 and the        covered stent 174 are removed from the press fixture 186 and        positioned in room temperature water for cooling; and    -   The first and second layers of elastomeric tube 342, 380 are        removed from the smooth covered stent 198.

It will be appreciated by those skilled in the art that changes could bemade to the examples described above without departing from the broadinventive conceptive therefor. For example, heat and pressureapplication steps of one example may be used with the expansion andremoval steps of the elastomeric tube 116 of a different example toencapsulate the stent 100 with a smooth covering. It is understood,therefore, that this invention is not limited to the particular examplesdisclosed, but it is intended to cover modifications within the spiritand scope of the present invention as defined by the appended claims.

1-20. (canceled)
 21. An encapsulated stent graft comprising asubstantially tubular body comprising: a luminal surface; an abluminalsurface; a balloon expandable stent having an inner surface and an outersurface; an inner cover covering the inner surface of the balloonexpandable stent, the inner covering comprising: a first layerconsisting essentially of a first material having a porous structure anda melting point and a second material, different from the first materialand parallel to the first porous material, within the first layer andhaving a melting point lower than the melting point of the first porousmaterial of the first layer, and a second layer over the first layerconsisting essentially of a first material having a porous structure anda melting point and a second material, different from the first materialof the second layer, parallel to the first porous material within thesecond layer and having a melting point lower than the melting point ofthe first porous material of the second layer, wherein the firstmaterial of the first layer is the luminal surface of the stent graft,the first material of the second layer contacts the first material ofthe first layer and the second material of the second layer, the secondmaterial of the second layer contacts the stent, and the second materialof the first layer, upon the application of heat sufficient to melt thesecond material of the first layer, flows into the porous structure ofthe first material of the first layer and the porous structure of thefirst material of the second layer thereby forming a bond between thefirst material of the first layer and the first material of the secondlayer; and an outer cover covering the outer surface of the balloonexpandable stent, the outer cover comprising; a first layer consistingessentially of a first material having a porous structure and a meltingpoint and a second material, different from the first material, parallelto the first material within the first layer and having a melting pointlower than the melting point of the first material of the first layer,and, a second layer over the first layer consisting essentially of afirst material having a porous structure and melting point and a secondmaterial, different from the first material of the second layer,parallel to the first material within the second layer and having amelting point lower than the melting point of the first material of thesecond layer, wherein the second material of the first layer contactsthe stent and the first material of the first layer, the first materialof the second layer is the abluminal surface of the stent graft, andsecond material of the second layer, upon the application of heatsufficient to melt the second material of the second layer, flows intothe porous structure of the first material of the first layer and theporous structure of the first material of the second layer therebyforming a bond between the first material of the first layer and thefirst material of the second layer.
 22. The stent graft of claim 21,wherein the first material of the first layer and the second layer ofthe inner cover and the first material of the first layer and the secondlayer of the outer cover is selected from PTFE, esPTFE and ePTFE. 23.The stent graft of claim 22, wherein the second material of the firstlayer and the second layer of the inner cover and the second material ofthe first layer and the second layer of the outer cover is selected fromFEP and polyurethane.
 24. The stent graft of claim 21, wherein the firstmaterial of the first layer and the second layer of the inner cover isesPTFE and the second material of the first layer and the second layerof the outer cover is polyurethane.
 25. The stent graft of claim 21,wherein the first material of the first layer and the second layer ofthe inner cover is ePTFE and the second material of the first layer andthe second layer of the outer cover is polyurethane.
 26. The stent graftof claim 21, wherein the first material of the first layer and thesecond layer of the inner cover is esPTFE and the second material of thefirst layer and the second layer of the outer cover is FEP.
 27. Thestent graft of claim 21, wherein the first material of the first layerand the second layer of the inner cover is ePTFE and the second materialof the first layer and the second layer of the outer cover is FEP. 28.The stent graft of claim 21, wherein each of the inner cover and theouter cover each further include one or more additional layersconsisting essentially of a first material having a porous structure anda melting point and a second material, different from the firstmaterial, parallel to the first material having a melting point greaterthan the melting point of the second material and wherein in each of theone or more additional layers the first and second materials are in analternating pattern.
 29. An encapsulated stent graft comprising asubstantially tubular body comprising: a luminal surface; an abluminalsurface; a balloon expandable stent having an inner surface and an outersurface; an inner cover covering the inner surface of the balloonexpandable stent, the inner covering comprising: a first layerconsisting essentially of a first material selected from PTFE, ePTFE andesPTFE, and a second material parallel to the first material selectedfrom FEP and polyurethane and having a melting point lower than amelting point of the first material of the first layer, and a secondlayer over the first layer consisting essentially of a first materialthat is the same as the first material of the first layer and a secondlayer parallel to the first material that is the same as the secondmaterial of the first layer and having a melting point lower than themelting point of the first material of the second layer, wherein thefirst material of the first layer is the luminal surface of the stentgraft, the first material of the second layer contacts the firstmaterial of the first layer and the second material of the second layer,the second material of the second layer contacts the stent, and thesecond material of the first layer, upon the application of heatsufficient to melt the second material of the first layer, is a bondbetween the first material of the first layer and the first material ofthe second layer; and an outer cover covering the outer surface of theballoon expandable stent, the outer cover comprising; a first layerconsisting essentially of a first material selected from PTFE, ePTFE andesPTFE, and a second material parallel to the first material selectedfrom FEP and polyurethane and having a melting point lower than amelting point of the first material of the first layer, and a secondlayer over the first layer consisting essentially of a first materialthat is the same as the first material of the first layer and a secondlayer parallel to the first material that is the same as the secondmaterial of the first layer and having a melting point lower than themelting point of the first material of the second layer, wherein thesecond material of the first layer contacts the stent and the firstmaterial of the first layer, the first material of the second layer isthe abluminal surface of the stent graft, and second material of thesecond layer, upon the application of heat sufficient to melt the secondmaterial of the second layer, is a bond between the first material ofthe first layer and the first material of the second layer; and whereinthe luminal and abluminal surfaces of the stent graft have no visiblecreases or ridges.
 30. The stent graft of claim 29, wherein each of theinner cover and the outer cover each further include one or moreadditional layers consisting essentially of a first material that is thesame as the first material of the first and second layers and a secondmaterial that is the same as the second material of the first and secondlayers and each of the one or more additional layers the first andsecond materials are in an alternating pattern.